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Charles Dharapak, Associated Press
Sen. John McCain, R-Ariz., left, and President Bush walk down the West Wing colonnade.

While the Democratic candidates traded insults Wednesday and tensions escalated over how and when the contest might end, President Bush passed the mantle of the Republican Party's future to John McCain.

The one-time adversaries stood united in the Rose Garden as the president praised the Arizona senator, pledging to do whatever he could to help keep the Oval Office occupied by a Republican.

"John showed incredible courage and strength of character and perseverance in order to get to this moment," Bush said, a day after McCain clinched the GOP nomination. "And that's exactly what we need in a president: somebody that can handle the tough decisions; somebody who won't flinch in the face of danger."

Dismissing a suggestion that his low approval ratings could be a drag on the Republican ticket, Bush said voters are "not going to be voting for me."

McCain said he was honored and humbled by Bush's endorsement and said he looked forward to campaigning with him.

"I'll be pleased to have him with me both from raising money and the much needed finances for the campaign, and addressing the challenging issues that face this country," McCain said.

So far both of his possible Democratic opponents, Hillary Rodham Clinton and Barack Obama, have raised far more money than McCain.

The day after Clinton catapulted herself back into contention for the Democratic nomination by winning the Ohio, Texas and Rhode Island primaries, she questioned Obama's credentials to be president on six morning talk shows, though she acknowledged the possibility of a joint ticket.

Obama matched her with six TV appearances of his own and said she had failed her biggest test by approving the Iraq war.

Clinton was asked twice on TV about the possibility of herself and Obama on the ticket this fall. She told CBS that may be "where this is headed. But, of course, we have to decide who's on top of the ticket." Obama also called such talk premature.

Tuesday's voting gave Clinton a net gain of 12 delegates, according to The Associated Press. The AP's tally puts Obama ahead with 1,567 delegates to Clinton's 1,462.

Clinton says it's not math, it's momentum. "What's important here is this campaign has turned a corner," she said on CNN.

Both candidates will spend the weekend campaigning. Clinton travels today to Mississippi, which will hold a primary Tuesday. Obama will spend Friday in Wyoming, on the eve of that state's Democratic caucuses.

In other campaign news Wednesday:

• Clinton called for the Democratic National Committee to restore Michigan's 210 convention delegates and Florida's 156. The states are being penalized for holding primaries ahead of the party schedule. Clinton, who won both states' primaries, said, "I think Florida and Michigan should count."

Howard Dean, chairman of the Democratic National Committee, discouraged that line of thinking. "We are not going to change the rules in the middle of the game," he said in a statement.

One possibility, according to DNC spokeswoman Stacie Paxton, is for both states to hold new vote-by-mail primaries.

The Florida Democratic Party has "a very detailed proposal" on how to do that, spokesman Mark Bubriski said. Obstacles include no sign so far that the candidates are open to a new primary and a cost Bubriski says could reach $6 million.

• McCain would lose to either of his Democratic rivals if the national election were held now, according to a Washington Post-ABC News poll released Wednesday.

McCain would receive 40 percent of the vote compared with 52 percent for Obama, according to the poll. McCain would lose to Clinton 44 percent to 50 percent, the poll said.

McCain clinched the Republican nomination in Tuesday's primaries.

The survey of 1,126 people, conducted between Feb. 28 and March 2, has a margin of error of plus or minus 3 percentage points, and 4 points among Democratic-leaning independents.

Contributing: Aliza Marcus, Bloomberg News