Mitt Romney. AP Photo/Richard Drew

Some of the most influential members of the Republican Party are planning to sit out Donald Trump's coronation at the Republican National Convention this summer.

Since Trump virtually sealed up the Republican presidential nomination on Tuesday, the last several Republican presidential nominees — and the last two Republican presidents — have all announced plans to skip the convention.

An aide to 2012 nominee Mitt Romney confirmed to Business Insider on Thursday that the former Massachusetts governor will not be attending the convention. The Romney news was first reported by The Washington Post.

Sen. John McCain, the party's 2008 nominee, has also said that he would be skipping the convention. McCain is facing a tough reelection campaign for his seat.

And on Wednesday, former Presidents George W. Bush and George H.W. Bush said that they would not endorse in the 2016 campaign and would skip their party's convention.

Many of the influential Republicans clashed directly with Trump and actively supported other candidates in the 2016 primary.

Both former presidents campaigned actively for former Florida Gov. Jeb Bush. And Romney, who briefly considered a 2016 bid himself, stumped for Ohio Gov. John Kasich and supported Sen. Ted Cruz, citing the necessity to deny Trump the presidency.

"His domestic policies would lead to recession," Romney said of Trump during a fiery speech in March. "His foreign policies would make America and the world less safe. He has neither the temperament nor the judgment to be president. And his personal qualities would mean that America would cease to be a shining city on a hill."

McCain is already feeling the effects of Trump's nomination.

In leaked audio obtained by Politico, McCain detailed the electoral difficulties Trump poses that will likely make his Senate reelection bid this fall what he termed the "race of my life."

McCain said, according to Politico:

If Donald Trump is at the top of the ticket, here in Arizona, with over 30% of the vote being the Hispanic vote, no doubt that this may be the race of my life. If you listen or watch Hispanic media in the state and in the country, you will see that it is all anti-Trump. The Hispanic community is roused and angry in a way that I've never seen in 30 years.