By TOM LOBIANCO, ASSOCIATED PRESS
INDIANAPOLIS -- The face of Indiana politics for nearly four decades, Republican Sen. Richard Lugar is battling for political survival against a tea party-backed GOP challenger who says the senator has become more interested in compromising with liberals in Washington than representing conservatives back home.
With Mitt Romney expected to coast to victory in three GOP presidential primaries, Lugar's re-election fight - the toughest in his 36-year career - is the highest-profile contest in four states with voting Tuesday.
Wisconsin Democrats were preparing to pick a candidate to run against Republican Gov. Scott Walker in just the third gubernatorial recall election in U.S. history. In North Carolina, voters were considering a referendum that would effectively ban same-sex marriages.
Although polls in Indiana signaled momentum for the challenger, Lugar hoped a heavy turnout would propel him to victory against Indiana Treasurer Richard Mourdock.
"If they come, we will win," Lugar said.
However, absentee voting lagged nearly 40 percent behind that of four years ago, when Barack Obama and Hillary Rodham Clinton crisscrossed Indiana in their clash for the Democratic presidential nomination.
Although Lugar's best shot at victory appeared to be wooing Democrats and independents to take a Republican ballot and vote for him, that strategy also fueled Mourdock's argument that the incumbent, known for his genial demeanor and reputation as a diplomat, has become too moderate.
During a campaign stop Monday in Elkhart, the challenger said his supporters were eager to get to the polls.
"We have over 1,300 precincts where we will have volunteers working for all 12 hours," Mourdock said. "We have a tremendous grassroots game."
Lugar entered the race with a huge fundraising advantage over Mourdock but saw a sharp reversal of fortune in recent months, as outside groups spent millions on ads pounding away at his voting record and his failure to keep a home in Indiana.
Kip Tew, a former state Democratic Party chairman, said he didn't expect a surge of Democrats turning out for Lugar. The recent wave of TV attack ads from the Lugar campaign against Mourdock has "ruined Dick Lugar's brand in the state," he said.
"You might not see as much as if Sen. Lugar had made a positive appeal to being a statesman and trying to govern from the center," Tew said.
The winner will face Democratic Rep. Joe Donnelly in November.
Romney, the presumptive Republican nominee, has no serious challengers left in Tuesday's Indiana, West Virginia and North Carolina primaries. Former Pennsylvania Sen. Rick Santorum dropped out in April and former House Speaker Newt Gingrich left the race last week. Texas Rep. Ron Paul is still contesting the nomination, but he lags far behind in the delegate count.
Romney is 288 delegates shy of officially clinching the Republican nomination, according to an Associated Press count. There are 107 delegates at stake Tuesday, and Romney could win about 100 if he does well.
The former Massachusetts governor struggled through a prolonged primary this winter and spring, fending off challenges from the right, particularly in Southern states. But Romney all but sealed the contest after a win in Wisconsin's primary in early April. Santorum decided to leave the race ahead of the primary in his home state of Pennsylvania and endorsed Romney in an email to supporters Monday night.
"The primary campaign certainly made it clear that Gov. Romney and I have some differences. But there are many significant areas in which we agree," Santorum wrote, citing common ground in economic, social and foreign policy.
He added: "Above all else, we both agree that President Obama must be defeated. The task will not be easy. It will require all hands on deck if our nominee is to be victorious. Gov. Romney will be that nominee and he has my endorsement and support to win this the most critical election of our lifetime."
According to recent Wisconsin polls, Milwaukee Mayor Tom Barrett leads former Dane County executive Kathleen Falk in the race to run as Democratic candidate for governor in a historic recall election. The recall vote against Republican Gov. Walker stems largely from his successful push to end nearly all collective bargaining rights for most state workers.
Walker, who has emerged as a conservative hero, shattered state campaign finance records, raising $25 million in an effort to keep his job. He is on the Republican primary ballot but faces only token opposition.
In North Carolina, voters were considering a referendum that would define marriage as between a man and a woman, effectively slamming the door on same-sex marriages. Political observers expected the measure to pass.
In the campaign's final days, Obama Cabinet members voiced support for same-sex marriage and former President Bill Clinton lent his voice to robocalls opposing the amendment. Evangelist Billy Graham, 93, has been featured in full-page newspaper ads backing the gay-marriage ban.
Below, more Tea Party Senate candidates: