President Bush endorsed Sen. John McCain on Wednesday as winner of the Republican presidential nomination and said he will campaign for the Republican ticket as much as McCain wants.

With the two standing in the sun at the edge of the White House Rose Garden, the Arizona senator said he welcomed Bush's support.

Reflecting his low standing in polls - only about 30 percent of those surveyed approve of his job performance - Bush and his aides made liberal use of an old political joke: offering Bush's support, or, if McCain preferred, his opposition.

"Either way, I want him to win," the president said.

Playing down his role - and potential influence - Bush added: "They're not going to be voting for me."

The party leader's official recognition of McCain's success in the Republican primary campaign is remindful of the roller-coaster relationship Bush and McCain have had for nearly a decade, after they competed strenuously - and at times bitterly - to become the party's nominee in the 2000 presidential election.

McCain moved to patch up their differences, campaigning for Bush in the general elections in 2000 and 2004, moderating some of his stands on social issues to more closely match Bush's and speaking out in support of the increased troop deployment in Iraq that Bush announced in January 2007.

After the two had lunch in the president's private dining room, Bush focused on McCain's return from the near-death of his campaign last year and said the senator had demonstrated the sort of "strength of character and perseverance" demanded of a president.

McCain said he was humbled by Bush's support and said several times that he looked forward to Bush's making time to campaign for him.

Hoping to spoil the GOP party, Democrats wasted no time in tagging McCain's candidacy as a continuation of the Bush presidency.

"John McCain just doesn't get it," said Howard Dean, the Democratic Party chairman. "All he offers is four more years of the failed Bush economy, an endless war in Iraq and shameless hypocrisy on ethics reform. The fact is, the American people want change, not another out-of-touch Bush Republican, and Democrats welcome the opportunity to draw this contrast for voters."

In a related matter, a Democratic-leaning group financed by a major labor union and wealthy liberal activists is running ads against McCain in Ohio and Pennsylvania.

The ad portrays McCain and Bush as interchangeable on key issues such as Iraq, tax cuts and health care. Its message echoes a theme Democrats have been developing against McCain - trying to link him as closely to Bush's policies as they can.

"A trillion dollars in Iraq over the next 10 years, McSame as Bush," an announcer in the ad says. "A millionaire who's for tax cuts for millionaires. McSame as Bush. Oil companies? They get tax breaks while we pay at the pump. McSame as Bush. Absolutely no plan for universal health care. McSame as Bush. Tell John McCain we need a new direction. Not the McSame old thing."

The ad is the work of the Campaign to Defend America, a nonprofit organization that is among anti-war and left-of-center groups that have pledged a multimillion-dollar campaign to target McCain and congressional Republicans on the consequences of the Iraq war on the U.S. economy.

Also Wednesday, a new Washington Post-ABC News poll shows McCain trailing both potential Democratic nominees in hypothetical matchups.

Illinois Sen. Barack Obama leads McCain by 12 percentage points among all adults in the poll. Sen. Hillary Rodham Clinton of New York has a six-point lead in the poll.

One obstacle for McCain might be his age. More than a quarter of those polled said they are less inclined to support the 71-year-old because, if elected, he would be the oldest person ever to become president. The percentage discouraged by McCain's age is more than double the numbers who would be less enthusiastic about supporting Obama due to his being an African American or Clinton because she is a woman.