As Mitt Romney and Donald Trump today reunite in Las Vegas for a glitzy campaign fundraiser, President Obama's re-election team is knocking the presumptive GOP nominee for not condemning Trump's "birtherism."

The real estate mogul, who endorsed Romney in February and is a top surrogate, recently reiterated the fact-challenged claim that Obama was not born in the U.S. and, by implication, that he is a constitutionally illegitimate president. Romney says he disagrees with Trump but won't condemn him for his views.

A new web video by the Obama campaign contrasts Romney's reaction to Trump with Sen. John McCain's response to similar rhetoric during the 2008 campaign.

"As the Republican nominee, John McCain stood up to the voices of extremism in his party," the video says.

McCain appears in two video clips from town hall meetings when he publicly disavowed statements from audience members questioning Obama's character and birthplace.

"I have to tell you. He is a decent person," McCain said of then-Sen. Obama in one clip. "And a person that you do not need to be sacred [of] as president of the United States."

When one woman calls Obama an Arab, McCain says, "No ma'am. He's a decent family man, citizen, that I just happen to have disagreements with."

The tagline of the video: "McCain and Romney: Two Republican nominees. Only one willing to lead."

Asked Monday about Trump's claims, Romney told reporters he doesn't agree with everything his supporters say but needs their support.

"You know I don't agree with all the people who support me and my guess is they don't all agree with everything I believe in," he said. "But I need to get 50.1 percent or more and I'm appreciative to have the help of a lot of good people."

UPDATE:  Romney campaign spokeswoman Amanda Henneberg further clarifies in an email:  "Governor Romney has said repeatedly that he believes President Obama was born in the United States. The Democrats can talk about Donald Trump all they want - Mitt Romney is going to talk about jobs and how we can get our economy moving again."