On one of the most symbolic days of the election — the day Romney will almost certainly clinch the Republican nomination — the former Massachusetts governor is counting on Donald Trump as a friend. Romney plans to stand shoulder to shoulder with Trump at a high-dollar Las Vegas fundraiser Tuesday night that is expected to raise millions for his campaign.

For their part, Team Trump welcomes Romney's friendship.

"It's telling that the standard bearer of the Republican Party continues to consider Donald Trump an important surrogate," Trump's special counsel, Michael Cohen, said in an interview with ABC News from Las Vegas.

The joint appearance has left critics scratching their heads after Trump, in recent interviews, has continued to question whether President Obama was born in the United States. Romney said he's confident that issue has been put to rest.

"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," Romney said in a brief interview on his campaign plane on Monday. "But I need to get 50.1 percent or more and I'm appreciative to have the help of a lot of good people."

Cohen, a top political aide to The Donald, said all the agitating about Trump was "a clear signal" that Romney's opponents were concerned about Trump's "massive popularity and his ability to raise substantial funds" for the GOP nominee between now and November.