WASHINGTON (AP) -- Barack Obama and Hillary Rodham Clinton fought for a breakout in their eyeball-to-eyeball Democratic duel while Republican John McCain hoped to bury his rival's presidential hopes in a blur of voting Tuesday from Alaska to the Atlantic.
An enormous cache of delegates was at stake - not enough to clinch a nomination but plenty enough to mint a runaway favorite, or even two.
The days of retail politicking in rustic diners was a distant memory, although just weeks old. Sens. Clinton and Obama each poured more than $1 million a day into TV ads in the last week alone; Clinton buying an hour on the Hallmark Channel for a town hall meeting on Monday night, Obama seeing some $250,000 disappear in 30 seconds in his Super Bowl ad a day earlier.
Clinton's voice was raspy from the ragged pace and she joked about her weariness on David Letterman's "Late Show." She didn't dare have a beer while watching the Super Bowl at a Minneapolis bar "only because I am so tired I thought I might still be there if I had."
Obama was stoic, too, telling a Hartford, Conn., rally, "I may be skinny, but I'm tough."
The electoral territory was vast and so were the stakes. Mitt Romney, his Republican bid on the line, boomeranged across the country and back in a 37-hour dash, branding himself the true Ronald Reagan conservative at every stop.
"I think you're going to see a growing crescendo of Republican conservatives getting behind my candidacy," the former Massachusetts governor said. He conceded: "Right now that hasn't entirely happened."
McCain struggled to close the sale with his party's base after coming strikingly far without its solid support. "I will preserve my proud conservative Republican credentials" while extending a practiced hand to Democrats, he promised.
Romney sought until the end to exploit the right's mistrust of McCain, an Arizona senator who opposed President Bush's tax cuts when they were introduced, departed from orthodoxy on immigration, favors mandates to slow global warming and led campaign finance reforms that activists say trampled on their speech rights.
McCain responded with a TV ad reminding people Romney had changed some stripes. It showed Romney in a 1994 debate calling himself "an independent during the time of Reagan-Bush. I'm not trying to return to Reagan-Bush."
Romney campaigned from Tennessee to California on the eve of the voting, only to turn back to attend West Virginia's nominating convention Tuesday. McCain, Obama and Clinton clustered in the hotly competitive Northeast.
Former Arkansas Gov. Mike Huckabee focused on the South, his continued candidacy an open question - as was Romney's viability, if he couldn't pull off surprises Tuesday.
After months when it was all about expectations and momentum, not to mention confusion, real numbers finally became important.
The two dozen contests Tuesday were delivering 1,023 Republican and 1,681 Democratic delegates. The number needed to win the nomination: 1,191 Republican and 2,025 Democratic.
John Edwards' departure after South Carolina's primary simplified the math but little else on the Democratic side.
Since winning that state, Obama has collected a succession of marquee endorsements - several of them named Kennedy - and pulled into a statistical tie with Clinton in a national poll and in California, Tuesday's biggest prize with 370 Democratic delegates.
The two were campaigning for history as well - Clinton seeking to become the first female president, Obama the first black one.
Little separates them on most issues, including universal health coverage, ending U.S. military involvement in Iraq and raising taxes on the rich. And neither has accounted fully for all their proposed spending.
Instead, the campaign has turned on her experience and his vision of change, debated intensely but with more civility in the latest round than when former President Clinton, purposefully or not, brought racial sensitivities to the surface in stumping for his wife.
Party rules were stacked against a Tuesday knockout for Democrats. All their primaries and caucuses were awarding delegates proportionately, so coming in second counted. In the Republican field, nine contests offered all delegates to the winner.
Among the most closely watched races:
-California, where Obama made up ground against longtime poll leader Clinton, and Romney bid for an upset. McCain planned to campaign there Tuesday after a morning rally at Rockefeller Center in New York.
State election officials said at least 3 million Californians already had voted, via mail-in ballot, out of 5.5 million ballots issued. They predicted that about 1 million of the remaining ballots would be cast Tuesday. Mail-in ballots are the last to be counted, increasing the odds of protracted suspense in the West.
-Missouri: A toss-up in both parties
-New York: Clinton's territory as senator, but Illinois Sen. Obama didn't concede it.
-New Jersey: Another state where the Democratic race tightened.
-New Mexico, Arizona: Along with California, states with large Hispanic populations, which to date have favored Clinton.
-Connecticut: A Democratic battleground.
-Georgia: A three-way toss-up among McCain, Romney and Huckabee.
McCain was favored in New York, New Jersey, Connecticut, Delaware and his home state of Arizona, with 251 delegates combined. Romney hoped to counter with victories in Utah and West Virginia, as well as in a string of caucuses in Western and Midwestern states.
Associated Press writers Beth Fouhy, Glen Johnson, Jim Kuhnhenn, Nedra Pickler, Libby Quaid and Liz Sidoti contributed to this report.
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