John McCain. REUTERS/Michael Dalder Sen. John McCain of Arizona issued a statement on Thursday agreeing with Mitt Romney's blistering critique of GOP presidential frontrunner Donald Trump.

"I share the concerns about Donald Trump that my friend and former Republican nominee, Mitt Romney, described in his speech today," McCain said.

McCain, his party's 2008 presidential nominee, added:

I would also echo the many concerns about Mr. Trump's uninformed and indeed dangerous statements on national security issues that have been raised by 65 Republican defense and foreign policy leaders.

Earlier in the day, Romney gave a fairly unprecedented speech in which he eviscerated his own party's leading presidential contender. Romney, the GOP nominee in 2012, called Trump a "phony," a "fraud," a "con man," and "fake."

"His domestic policies would lead to recession," Romney said. "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 said he agreed with Romney's foreign-policy criticisms in particular.

"I want Republican voters to pay close attention to what our party's most respected and knowledgeable leaders and national security experts are saying about Mr. Trump, and to think long and hard about who they want to be our next commander in chief and leader of the free world," McCain said.

For his part, Trump has repeatedly dismissed Romney as a failed candidate acting on behalf of a desperate Republican establishment.

Trump ignited a firestorm last summer when he briefly disputed the idea that McCain, a former Vietnam War POW, was a "war hero."

Trump infamously quipped that he liked "people that weren't captured."