Mitt Romney to join Donald Trump in Las Vegas

Tuesday night, Mitt Romney joins 'The Donald' under the bright lights of Las Vegas - but some say there's a roulette-style risk as Trump continues his 'birther' attacks on Obama.

Team Obama on Tuesday unleashed this ad: It shows 2008 GOP presidential candidate John McCain dismissing similar claims. McCain calls Obama a “decent family man” after a woman yells that Obama is “an Arab.”

The Obama campaign is asking Romney to do the same.

Critics say there's no good side to appearing with Trump. Romney can raise his own money.

"The cost of appearing with this bloviating ignoramus is obvious it seems to me,” says George Will. “I don't understand the benefit."

Meanwhile, some presumed good news for Romney. Texas votes Tuesday and should give him the 1,144 delegates needed to win the nomination, speeding up speculation about who will join him on the ticket.

WTOP Tuesday asked Virginia Governor Bob McDonnell about his chances.

He insisted the two haven't broached the subject; he just wants Romney to win.

"That's my goal and I'll let Mitt Romney decide who he wants to be VP,” he says. “That's not my call."