A final rash of opinion polls suggested fresh opportunities and potential perils for Republican and Democratic candidates, and the campaigns adjusted their strategies accordingly.
Former Massachusetts Gov. Mitt Romney flew to California for a Monday night stop in Long Beach amid signs of inroads against Sen. John McCain of Arizona, the national Republican front-runner.
Sens. Hillary Rodham Clinton of New York and Barack Obama of Illinois campaigned across the Northeast as their top strategists looked beyond today to the prospect of a fight to the Democratic National Convention this summer.
"Many of us will be making our reservations for Texas and Ohio and perhaps Pennsylvania and beyond that," Howard Wolfson, a senior Clinton strategist, said in reference to March and April contests.
Today is unlike any balloting before. Twenty-four states, from New York to California, will hold primaries or caucuses; 22 on the Democratic side and 21 for Republicans, with hundreds of nominating delegates at stake on both sides.
The results could be decisive for Republicans, given winner-take-all rules in most of the contests designed to quickly winnow the field and crown a nominee. For Democrats, the prospects are for more of a muddle, as most delegates are awarded on a proportional basis that could reward Clinton and Obama in their respective pockets of strength: she among working-class voters, women and Latinos; Obama among young voters, the more affluent and African Americans.
Romney's nighttime rally in Long Beach served to focus the Republican race on California, by far the day's biggest prize.
"This is a pivotal race, and the course of America is going to be set by what happens" in the California contest, Romney told hundreds of supporters gathered at a Long Beach Airport hangar. Asked earlier in the day whether he would remain in the race if he didn't do well there or in another large state, Romney said only that he predicted victory.
He spent most of his day campaigning in the South, where he pressed his case that he, not McCain, was the true conservative in the race.
"Do you want a nominee who voted against the Bush tax cuts?" Romney asked dozens of diners eating buttermilk pancakes and grits and sipping coffee at a diner near Vanderbilt University. "Noooooo!" they cried. "Do you want to have a nominee who represents the conservative principles and keeps us inside the house that Ronald Reagan built?" he asked, and the crowd cheered in affirmation.
McCain, reflecting his confidence, spent a second day in Romney's home state. In Boston, he appeared at Faneuil Hall alongside two of Romney's gubernatorial predecessors, Paul Cellucci and Jane Swift. McCain questioned rising costs in the Massachusetts health insurance program that Romney helped create.
"It doesn't surprise me. Entitlement programs like this always increase in size," McCain said.
His aides seemed anxious about polls suggesting a close California finish; McCain added a San Diego appearance with Gov. Arnold Schwarzenegger today. Originally, his plans included stops only in New York and Arizona.
McCain also began airing a tough new TV spot, excerpting Romney's appearance in a 1994 debate with Sen. Edward M. Kennedy of Massachusetts in which Romney called himself an independent and declared, "I'm not trying to return to Reagan-Bush."
Sweeping through New Jersey and New York -- where he picked up the endorsement of former Empire State Gov. George E. Pataki -- the famously superstitious McCain shied away from bold predictions. "I have seen this movie before," he told reporters, alluding to his own political ups and downs.
Still, McCain spent much of the time on his campaign bus discussing the general election -- including how the debate over the Iraq war might be different in November and the states where he will campaign. McCain said he hadn't thought about whether he would quit the U.S. Senate if he became the Republican nominee.
Former Arkansas Gov. Mike Huckabee, meantime, continued to stump in his native South. He appealed to working-class voters and took a veiled shot at Romney for turning more conservative as he began to run for president.
"Being president is not just a job. It's a sacred trust," Huckabee told about 600 people at an airport rally in Texarkana, Ark., the Associated Press reported. "People give you the trust of that office, and people need to know what you say is what you really believe and there's clarity to your convictions."