Barack Obama rebuked Hillary Clinton for "saber-rattling" on Iran, but her camp claimed he was "running scared," two days before their next fateful date with Democratic voters.
The White House rivals injected more bile into their attacks before primaires in Indiana and North Carolina, where Obama hopes to land a knockout, and Clinton hopes to ignite her long-odds comeback bid.
Both spent the day hop-scotching through rust-belt Indiana, sparring with one another, and beseeching supporters to ensure a high turnout.
Clinton delighted patrons by showing up at a Dairy Queen ice cream store, while Obama held a giant picnic with his family, as his six-year-old, Sasha urged people to "Vote for Daddy."
The former first lady was asked on ABC television whether she had any regrets about threatening to "totally obliterate" Iran if it used nuclear weapons against Israel.
"Why would I have any regrets? I am asked a question about what I would do if Iran attacked our ally, a country that many of us have a great deal of, you know, connection with and feeling for," she said.
But Obama accused Clinton of emulating what he called President George W Bush's "foreign policy of bluster and saber-rattling and tough talk."
The Clinton campaign took hope from polls showing the rivals locked in a close race in Indiana and cutting Obama's once huge lead in North Carolina.
Clinton spokesman Phil Singer said "it's clear the Obama campaign is running scared right now."
"They're currently watching our candidate catch fire on the stump and generate a significant amount of momentum going into election day."
The Obama campaign hit back though with an ad excoriating Clinton's call for a temporary moratorium on federal gasoline taxes, which the Illinois senator has ridiculed as a "gimmick."
"More low road attacks from Hillary Clinton," the ad's narrator says. "Clinton aides admit it won't do much for you -- but would help her politically."
Obama made a fresh attempt to quell a controversy sparked by racially tinged comments by his former pastor Jeremiah Wright, which rattled his campaign in a miserable April.
He accused Wright of putting "gasoline on the fire" last week with a combative round of public appearances, and said the Reverend's statements were "fundamentally" at odds with his own vision.
A new CBS/New York Times poll suggested he may be making some headway, giving Obama an 11 point lead over Republican candidate John McCain, 51-40, percent in a hypothetical general election matchup. On Tuesday, at the height of the latest furor over Wright, the contest had been tied.
Clinton led McCain in the same poll by 12 points.
The former first lady trails Obama in nominating contests and pledged delegates, so her last hope is to persuade Democratic party bosses known as superdelegates, that Obama is too risky to run against McCain in November.
"When the process finishes in early June, people can look at all the various factors and decide who will be the strongest candidate," Clinton, 60, said at the ABC town-hall meeting in Indianapolis, Indiana.
"I feel like I am going to be able to stand up to Senator McCain," said Clinton, who has promised a "game-changer" on Tuesday, after which only six contests will be left in the Democrats' exhausting nominating marathon.
Conventional wisdom has it that Clinton has to at least win Indiana to stop a stampede of superdelegates towards Obama, and to stay in the race.
If she could somehow pull off a suprise win in North Carolina, she could change the whole dynamic.
A new Zogby poll gave Obama the lead in North Carolina -- 48 percent to Clinton's 39. But the race in Indiana, a true battleground, was much tighter with him on 43 per cent to her 41, well within the four-point margin of error.
Clinton led an average of recent polls in Indiana by RealClearPolitics.com by nearly six points.
In a pan-Pacific warmup for Tuesday, Obama eked out a victory in Guam's caucuses by seven votes on Saturday, meaning the four pledged delegates up for grabs will likely be shared.