McCain gets formal Bush endorsement

John McCain went to the White House today for lunch with President Bush -- and for his formal blessing.

The Arizona senator, who hopes to succeed him in the White House, mathematically clinched the Republican nomination by sweeping Tuesday's primaries.

UPDATED: Bush said he was proud to support McCain, calling him a man with both "determination to defeat the enemy" and a "big heart" who cares about the less fortunate.

The president said that McCain showed "incredible courage and perseverance" to survive, come back, and secure the nomination. "That's exactly what we need as president," Bush said.

McCain said he was "honored and humbled" to receive the endorsement from someone for whom he said he holds "great admiration." He also said he wants Bush to campaign with him as much as possible, and Bush said he will help raise money and appear as much as he wants.

McCain said he received congratulatory calls Tuesday night from Democrats Barack Obama Hillary Clinton and pledged a "respectful campaign."

Asked about voters' thirst for change, Bush replied, "Every candidate's got to say change." But he said there's one thing that's essential not to change: the fight against terrorism. "There's still an enemy that lurks," Bush said.

The president also deflected questions about whether his unpopularity could hurt McCain's candidacy.

"They're not going to be voting for me," he said. "It's not about me. I've done my bit."

Still, McCain faces a delicate dance.

He has tied himself to key Bush administration policy, including on the Iraq war and on extending tax cuts. But both the Democratic contenders are already warning that a McCain presidency would be equivalent to a third Bush term, when polls show that voters want change.

A Democratic group is already launching a TV ad campaign -- independent from the candidates -- that says that McCain would be the "McSame." The ad shows McCain in a thumbs-up pose, but then puts the head of Bush on the body, and the heads of Bush and McCain alternate as the narrator says they hold the same position on Iraq, the economy, healthcare, and energy policy.

"Tell John McCain we need a new direction," the announcer concludes. Watch the ad below: