WASHINGTON -- The close race for majority control of the Senate comes down to whether Republican candidates in Massachusetts and Connecticut can win over President Barack Obama's voters and Democrats from Indiana to Arizona can impress Mitt Romney's GOP backers.

Ticket-splitting is vital to the prospects of Senate candidates in a half-dozen races in states that Obama and Romney are expected to win handily. These candidates are significantly outdistancing their parties' presidential nominees in polls, turning what should be an election-year rout into too-close-to-call contests.

With about three weeks to the Nov. 6 vote, Democrats hold a slight edge in keeping their majority in the Senate. GOP hopes have faded in New Mexico and Hawaii while incumbents in Florida and Ohio withstand an onslaught of outside spending to run ahead of their struggling rivals. In an unlikely scenario, races in Indiana and Arizona, once considered certain GOP wins, are competitive.

"The map has expanded over the election cycle," said Guy Cecil, executive director of the Democratic Senatorial Campaign Committee, who credited the class of recruits. "When the cycle started no one gave Democrats a shot at holding the majority."

Still, the mathematical equations of the election remain unchanged.

Democrats hold a 53-47 advantage in the Senate, counting the two independents, and must defend 23 seats to the GOP's 10. The Republicans need a net of four seats to grab the majority if Obama wins and a net of three if Romney captures the White House and Paul Ryan as vice president breaks a Senate tie.

Republicans are counting the open seat in Nebraska as a pickup and are bullish about holding Nevada despite a concerted Democratic effort. They're also upbeat about snatching Democratic seats in close contests in Virginia, Montana and North Dakota. Romney's first debate performance energized the party for the home stretch.

"There's renewed enthusiasm on our side," said Rob Jesmer, executive director of the National Republican Senatorial Committee. "It's filtered down to our Senate candidates. There's very good movement across the board."

In the lineup of ticket-splitting races to watch, one of the biggest surprises and promising opportunities for the GOP in the closing weeks of the campaign is Connecticut.

Former professional wrestling executive Linda McMahon, in her second Senate bid, is running even with three-term Democrat Rep. Chris Murphy in the Democratic-leaning state.

The wealthy McMahon is financing her ads, forcing the DSCC to spend $2 million and counting in a state that's solidly in the Obama column. This past week, the Democratic committee bought an additional $650,000 in ads while the Democratic group Majority PAC invested more than $500,000 to air spots to help Murphy. It's money the Democrats certainly would rather spend elsewhere.

The Republican nominee, who is on the air in the expensive New York City market, is using commercials to argue that she is not beholden to either party.

"Linda is an independent-minded leader who won't be swayed by partisan politics," says a woman in a testimonial commercial for McMahon. "Linda will be an independent voice in the Senate for all of us," says another woman.

Although Obama won Indiana in 2008, it's unlikely this year as Romney seems a probable winner along with Republican Rep. Mike Pence in his gubernatorial bid.

Yet Democratic Rep. Joe Donnelly is in a close race with Republican Richard Mourdock, a tea party favorite who unseated six-term Sen. Richard Lugar in the May primary. Donnelly has played up his moderate voting record in the House as a contrast to Mourdock. The Republican famously said after beating Lugar that bipartisanship meant Democrats siding with Republicans and that winning meant he would "inflict my opinion on someone else."

Indiana is a "conservative state but a state that looks for results, not strident partisanship, in the tradition of Richard Lugar and Evan Bayh," Donnelly said in an interview.

Lugar is backing the Republican but making no major effort to help the GOP candidate. Donnelly is hoping to sway some of the senator's GOP supporters, repeatedly referring to his work with the longtime lawmaker.

On Friday, Donnelly got some help from former President Bill Clinton who drew a crowd of 4,000 at the Hoosier Commonsense Rally.

"What is this idea that it's my way or the highway?" Clinton told the crowd. "I was raised to believe nobody's right all the time. Maybe Mr. Mourdock is, I don't know. He's way right all the time."

In Massachusetts, Republican Sen. Scott Brown also is talking bipartisanship in his race against Democrat Elizabeth Warren. Brown won a special election in January 2010 to fill the seat of the late Democratic Sen. Edward Kennedy, but this election he'll likely face 700,000 to 800,000 more voters, many Democrats or independents who favor Democrats.

Polls in the state show Obama with a hefty double-digit lead over Romney, a former Massachusetts governor. The same survey shows Brown and Warren in a tight race.

Not surprisingly, Brown tells viewers in a recent commercial, "To me, creating jobs is more important than what party you belong to. That's why one of the first votes I took as a senator was for a Democratic jobs bill."

Montana and North Dakota are expected to go for Romney, but split-ticket voting could lift first-term Democratic Sen. Jon Tester and Heidi Heitkamp, respectively. Republicans and Democrats say both have run near flawless campaigns to make their races highly competitive against a strong GOP political headwind.

Heitkamp, North Dakota's former attorney general, recently said she's "not in this for any reason other than solving problems."

"Our candidates have shown remarkable resilience," Cecil said. "Senate races are a choice between the two people on the ballot. They're affected by, but not determined by the presidential race."

The Democratic counterpoint to Connecticut is Arizona, where Democrat Richard Carmona, a former U.S. surgeon general, has surprised the GOP, riding a compelling up-from-the-bootstraps biography to a close race against Rep. Jeff Flake.

The National Republican Senatorial Committee recently purchased more than $130,000 of ad time, an investment that would have seemed unlikely two months ago. Rival ads about Carmona's character and temperament emerged this week, underscoring the increasingly tight contest.

In Maine, Republicans and GOP-leaning outside groups are running ads against independent Angus King, the former governor who is widely expected to caucus with the Democrats. Democrats are spending heavily on ads against Republican Charlie Summers. The Democratic candidate, Cynthia Dill, has the backing of state Democrats but has gotten little attention from national Democrats.

Americans Elect, a self-described non-partisan group that wanted to get a bipartisan presidential ticket on the ballot, recently purchased about $90,000 for direct mail in Maine in support of King.

Missouri remains a true wild card. Democratic Sen. Claire McCaskill, once considered the most vulnerable incumbent, got a fresh shot at re-election when Republican Rep. Todd Akin said women couldn't get pregnant in the case of "legitimate rape." Republicans, including Romney, called on him to quit the race.

Akin stayed in, securing the support of Newt Gingrich and Rick Santorum, state Republicans and a boost from religious leaders in a state that Romney should win easily. McCaskill recently launched a series of TV ads in which rape victims expressed outrage about Akin's remark and his opposition to emergency contraception.

Also on HuffPost:

Loading Slideshow...
  • 'The Stumble'

    Texas Governor Rick Perry's <a href="http://www.huffingtonpost.com/2011/11/09/rick-pery-forgets-federal-agencies_n_1085312.html" target="_hplink">inability to remember</a> the third agency he would cut as president had many predicting the untimely end of his campaign for president. Perry addressed his mental lapse before reporters after the debate, admitting, "Yeah I stepped in it man. Yeah it was embarrassing. Of course it was."

  • Romney's '$10,000 Bet'

    During a GOP primary debate in late 2011, Romney sought to put an end to then-presidential candidate Rick Perry's insistance that Romneycare was the basis of President Barack Obama's health care reform law. Perry launched in with an attack that he'd repeated before: "I'm just saying, you're for individual mandates, my friend," Perry said. "You've raised that before, Rick, and you're simply wrong," Romney responded, extending his hand toward Perry. "Rick, I'll tell you what: 10,000 bucks? $10,000 bet?" Perry declined, nothing that he wasn't a betting man, leaving Romney to quote a chapter from his book that he cited as proof he had never intended for his health care plan to be used as a national model.

  • Bachmann On Libya, Africa

    At a GOP primary debate in October of 2011, Michele Bachmann (R-Minn.) <a href="http://www.huffingtonpost.com/2011/10/18/michele-bachmann-libya-africa_n_1018814.html" target="_hplink">criticized</a> Obama's foreign policy decisions. "Now with the president, he put us in Libya," she said. "He is now putting us in Africa. We already were stretched too thin, and he put our special operations forces in Africa." Libya is, in fact, a country in Africa.

  • Awkward Silence

    During a 2010 gubernatorial debate, Arizona Governor Jan Brewer <a href="http://www.huffingtonpost.com/2010/09/02/jan-brewer-starts-badly-f_n_703559.html" target="_hplink">struggled to name</a> any of her accomplishments while introducing herself. "We have ... done so much ... We have um, did what was right for Arizona," she squeezed out after a long silent pause.

  • Can't Name Any Supreme Court Cases

    Christine O'Donnell was unable to name a single recent Supreme Court decision she disagreed with, when asked by moderator Nancy Karibjanian during a 2010 Delaware Senate debate. <a href="http://www.huffingtonpost.com/2010/10/13/christine-odonnell-stumped-supreme-court-debate_n_762067.html" target="_hplink">The dialogue</a>: <blockquote><strong>KARIBJANIAN</strong>: What opinions, of late, that have come from our high court, do you most object to? <strong>O'DONNELL</strong>: Oh, gosh. Um, give me a specific one. I'm sorry. <strong>KARIBJANIAN</strong>: Actually, I can't, because I need you to tell me which ones you object to. <strong>O'DONNELL</strong>: Um, I'm very sorry, right off the top of my head, I know that there are a lot, but I'll put it up on my website, I promise you.</blockquote>

  • Can I Call You Joe?

    When Sarah Palin and Joe Biden shook hands at the start of a 2008 vice presidential debate, Palin asked then then-Senator "Hey, Can I call you Joe?" "You can call me Joe," Biden replied. Palin <a href="http://www.politico.com/blogs/bensmith/0110/Two_versions_of_Can_I_call_you_Joe.html" target="_hplink">evidently kept confusing</a> then-Senator Joe Biden's last name with President Barack Obama's, referring to the VP candidate repeatedly as "O'Biden" in debate prep. Her staffers suggested she call him by his first name.

  • Change You Can Xerox

    Hilary Clinton's attempt at a jab toward President Barack Obama got her booed by the audience during a 2008 presidential debate. Clinton accused Obama of plagiarism in his popular speeches, saying "Lifting whole passages from someone else's speeches is not change you can believe in, it's change you can Xerox."

  • 'Likable Enough'

    During a Democratic presidential primary debate in early 2008, then-candidate Hillary Clinton was being pressed on surveys that suggested New Hampshire voters appreciated her resume, but found then-Sen. Barack Obama (D-Ill.) more likable. Clinton appeared to feign insult, drawing sympathetic applause and smiles from the crowd. "Well, that hurts my feelings," she said. "But I'll try to go on. "He's very likable," Clinton continued of Obama. "I agree with that. I don't think I'm that bad." Obama took a brief break from scribbling notes to weigh in. "You're likable enough, Hillary," Obama said tersely, not making eye contact with Clinton. He then returned to his notepad.

  • Al Gore's Sighing

    A 2000 presidential debate seriously hurt Al Gore's campaign when the cutaway shots caught him rolling his eyes and sighing audibly during George W. Bush's answers. Critics say behavior made Gore look elitist and unlikable in contrast with Bush's relaxed and folksy demeanor. Jon Stewart mocks Gore's sighs in The Daily Show clip above.

  • Let Me Finish

    Ross Perot may go down in history for his repeated interruptions of "let me finish" during a 1992 presidential debate. The behavior became fodder for SNL comedian Dana Carvey's Perot impression.

  • Glancing At His Watch

    George H. W. Bush was caught glancing at his watch during a 1992 presidential debate with Bill Clinton and Ross Perot. The now-famous move damaged Bush's campaign, making him look bored and impatient, <a href="http://www.usnews.com/news/politics/articles/2008/01/17/a-damaging-impatience" target="_hplink">reports say</a>. Bush snuck at peek at his watch again during his daughter-in-law Laura Bush's speech at the Republican convention in 2008.

  • Who Am I? Why Am I Here?

    When Independent Presidential candidate Ross Perot picked Vietnam War hero Admiral James Stockdale for his VP nominee, it created a rare three-person Vice Presidential debate in 1992. Stockdale was not a politician and not very well known. Attempting to introduce itself and poke some fun at this, he chose as his opening statement: "Who am I? Why am I here?" Stockdale later said he hoped to follow up the remarks with an explanation of his life, but never got to that point. Instead, the line left viewers wondering the same thing.

  • Dispassionate Death Penalty Response

    When the moderator of a 1988 presidential debate asked Governor Michael Dukakis if he would support the death penalty if his wife, Kitty Dukakis, was raped and murdered, Dukakis dispassionately responded, "No, I don't, Bernard, and I think you know that I've opposed the death penalty during all of my life." He then continued to talk about his stance. Some believe the lack of emotion or passion for the hypothetical situation cost Dukakis the election.

  • You're No Jack Kennedy

    In the 1988 Vice Presidential debate between Democratic VP candidate Senator Lloyd Bentsen and Republican VP candidate Senator Dan Quayle, Quayle was asked if his qualifications were sufficient to inherit the presidency, should it come to that. Quayle responded by comparing his experience level Jack Kennedy's experience level when he sought the presidency. The comparison prompted Bensten to say: "Senator, I served with Jack Kennedy. I knew Jack Kennedy. Jack Kennedy was a friend of mine. Senator, you're no Jack Kennedy." Quayle responded, "That was really uncalled for Senator."

  • No Soviet Domination

    In the 1976 presidential debate between Jimmy Carter and Gerald Ford, Ford famously stated "There is no Soviet domination of Eastern Europe." The remark came in response to a question about U.S. relations with the Soviet Union, a major concern in the Cold War era, and didn't sit well with an increasingly anti-Soviet public. Ford refused to back down from the claim even after the somewhat baffled debate moderator responded, "I'm sorry, what? ... Did I understand you to say, sir, that the Russians are not using Eastern Europe as their own sphere of influence in occupying most of the countries there and making sure with their troops that it's a communist zone?"

  • Sickly Nixon vs. Fit JFK

    The 1960 presidential debate between John F. Kennedy and Richard Nixon was the first nationally televised debate in the U.S. and <a href="http://www.time.com/time/nation/article/0,8599,2021078,00.html" target="_hplink">is thought to have</a> changed politics forever. The debate was historically declared a win for Kennedy by those who watched it on TV, and a win for Nixon for those who listened to it on the radio. Though the candidates were both strong on the issues, the visibly sweating Nixon looked sickly and pale compared to the young and fit Kennedy.