Conservative columnist George Will on Sunday questioned the judgement of presumptive Republican presidential candidate Mitt Romney, who will be campaigning with Donald Trump even after the billionaire recently said that the "truth" is that President Barack Obama was born in Kenya.

"I do not understand the cost-benefit here," Will told ABC's Jake Tapper. "The costs are clear. The benefits – what voter is going to vote for him because he’s seen with Donald Trump? The cost of appearing with this bloviating ignoramus is obvious, it seems to me."

"Donald Trump is redundant evidence that if your net worth is high enough, your IQ can be very low, and you can still intrude into American politics," he continued. "But, again, I don't understand the benefit. What is Romney seeking?"

"It's a long pattern," National Journal's Ron Brownstein agreed. "Mitt Romney, throughout the primary season, has shown very little willingness to confront the right. And there is a big portion of the conservative base of the Republican Party that does [falsely] believe that Barack Obama was not born in the U.S. ... Romney seems to be spooked throughout the whole process at the thought the right will mobilize against him."

"It's the broader point," Brownstein added. "When Rush Limbaugh called a Georgetown student a 'slut,' Romney was almost silent. When Rick Santorum said [John F.] Kennedy made him want to 'throw up,' Mitt Romney was silent."

Romney is scheduled to appear in Las Vegas on Tuesday at a private fundraiser hosted by Trump. Former Republican presidential candidate Newt Gingrich is also expected to be there. The Romney campaign has been encouraging supporters to donate for a chance to win dinner with Trump and the presumptive nominee.

Last week, Trump told The Daily Beast that Obama's former literary agent had erroneously said the president was born in Kenya because it was the "truth."

"He didn’t know he was running for president, so he told the truth," the billionaire mogul insisted. "He said he was born in Kenya and raised in Indonesia… Now they’re saying it was a mistake. Just like his Kenyan grandmother said he was born in Kenya, and she pointed down the road to the hospital, and after people started screaming at her she said, ‘Oh, I mean Hawaii.’ Give me a break."

Romney's senior adviser, Eric Fehrnstrom, on Friday defended the campaign's ties to Trump.

"You know, not too long ago, Jay Carney, the spokesman for the White House made a statement which I think is correct, and that statement was that a candidate can't be responsible for everything that their supporters say," Fehrnstrom told CNN.

"And in this case, Mitt Romney has made it clear that the place of the president's birth is not an issue for him. He accepts the fact that he was born in Hawaii. And we have many important challenges facing our country, and that's what we'd rather talk about."