UPDATE: CHECK HERE FOR SUPER TUESDAY RESULTS

On Super Tuesday (February 5th) voters across the country will head to the polls as primaries and caucuses get underway in over 20 states. Unlike in elections past, it is unclear whether a definitive winner will emerge from the pack at the end of the day.

Click here for Super Tuesday updates on Obama.

Click here for Super Tuesday updates on Clinton.

Click here for Super Tuesday updates on McCain.

Click here for Super Tuesday updates on Romney.

Keep reading for extensive Super Tuesday coverage.

The basic details of what's taking place:

In all, Democrats have primaries in 15 states and caucuses in seven states and American Samoa on Tuesday, with 1,681 delegates at stake.

Republicans hold 15 primaries, five caucuses and one state convention, and pick 1,023 delegates.

Ten of the Republican contests are winner-take-all.

CNN reports campaign spending could reach an unprecedented $20M in the rush to Tuesday:

Spending on political ads in the Super Tuesday states alone could reach an unprecedented $20 million, the Campaign Media Analysis Group estimates.... A vast majority of the spending -- nearly 90 percent -- is being done by the two remaining top-tier Democratic candidates: Sens. Barack Obama and Hillary Clinton....Obama spent $4 million on television advertising the last week of January, much of it going to advertising in the biggest Super Tuesday prize: California....Clinton spent over $3.5 million on television advertising the last week of January, CMAG estimated.

Obama has been campaigning hard in California and recently won the endorsement of a major Spanish-language newspaper in the state.

CNN notes that following Ted Kennedy's endorsement of Obama, Bill Clinton has begun to criticize Kennedy over his role in "No Child Left Behind"

Twice in the past two days, former President Bill Clinton has implied Massachusetts Sen. Ted Kennedy bears responsibility for the "No Child Left Behind" school standards, which are deeply unpopular with the Democratic base.

The statements come just days after Kennedy endorsed Hillary Clinton's primary opponent, Barack Obama.

In Arkansas yesterday, the former president told voters at a campaign stop that President Bush had "made a deal with Sen. Kennedy, and neither one of them meant to mess it up."

Romney's Super Tuesday strategy, according to the AP:

Republican Mitt Romney is conceding the bulk of the Northeast to rival John McCain, counting instead on his home state of Massachusetts, a split in California and wins in a series of caucus states to extend his presidential campaign beyond Super Tuesday.

Missing from Romney's latest campaign schedule were winner-take-all states of New York, New Jersey and Connecticut, which account for 180 of the 1,023 delegates at stake. The omissions were telling with voting in 21 GOP contests on Tuesday.

While popular with independents, McCain still has work to do to gain the support of the party's powerful conservative base:

As Super Tuesday looms -- and the possibility that McCain could all but wrap up the nomination -- the chattering conservative class is in an uproar. Talk show host Rush Limbaugh has warned that McCain as standard-bearer would destroy the Republican Party. Author and pundit Ann Coulter, in jaw-dropping heresy, said she would campaign for Democrat Hillary Rodham Clinton if McCain wins the party nod.

Surrogates for Romney have claimed that McCain is outside the GOP mainstream.

"If you are a Republican in the broadest sense, there is only one place to go right now, and that's Mitt Romney," said former Pennsylvania Sen. Rick Santorum.

According to MSNBC Obama's making a play for New Mexico:

New Mexico might be a Feb. 5 state to watch for Obama. The candidate made two stops in the state on Friday, in Albuquerque and Santa Fe -- an unusual amount of time to spend in just one state when the sand slips ever faster through the hourglass to Super Tuesday.

But New Mexico appears to be a key pick-up opportunity for Obama, who has six offices spread across the state. The campaign has shifted their Iowa get-out-the-caucus model to the several Feb. 5 states -- like New Mexico -- that will hold caucuses rather than primaries. The hope is that organizational strength can overpower Clinton's name recognition in these states. (It's worth noting, however, that while New Mexico is a technically a caucus, it operates more like a primary than the caucuses we saw in Iowa and Nevada.)

An estimated 20,000 people turned out for an Obama rally in Delaware on Sunday. The Washington Post reports:

Illinois Sen. Barack Obama flew from St. Louis to Delaware for a rally in Wilmington before returning to Chicago to watch the Super Bowl in the comfort of home with his family (and maybe some of his Secret Service agents, whom he said he'd invite in if they wanted).

An estimated 20,000 turned out for the rally at a downtown square in Wilmington, according to the fire department, with thousands who couldn't fit inside the square squeezing up against the perimeter fence and spreading onto the steps of surrounding buildings. It was the largest Wilmington rally city officials could remember.

UPDATE: CHECK HERE FOR SUPER TUESDAY RESULTS