Perennial Sunday show guest Sen. John McCain (R-Ariz.) went on CNN's "State of the Union," where host Candy Crowley asked him about the foreign policy differences within the Republican Party. McCain said of Sen. Rand Paul (R-Ky.), whom he once called a wacko bird for his stance on U.S. drone policy, that he "understood his appeal" to Americans “weary of involvement” in wars abroad. “Senator Paul is part of a wing of the [GOP] that’s been there ever since prior to World War I." He summed up the wing as advocating "a withdrawal to fortress America."

Sen. John McCain (R-Ariz.). (Joshua Roberts/Reuters)

A Pew Research Center poll from last year showed that most Americans think the United States should "mind its own business internationally."

McCain was asked to update his opinion on Paul's policies because of a piece that Texas Gov. Rick Perry wrote about his interpretation of America's role abroad.

In an op-ed in The Washington Post on Friday, the governor explicitly called out Paul's flavor of isolationism — especially in regard to how the United States should respond to developments in Iraq and Syria.

Paul is an articulate advocate for his views, which are shared by many on the left and some on the right. But in today’s world, with today’s threats, we still cannot “take blind shelter across the sea, rushing to respond only after freedom is lost.” That was President Reagan’s warning. Sen. Paul would be wise to heed it.

The Reagan reference is a subtle burn against an op-ed by Paul published in the Wall Street Journal last month, in which he wrote, "Like Reagan, I thought we should never be eager to go to war. And now, 11 years later, we are still dealing with the consequences."

When a Buzzfeed reporter asked Paul's chief adviser, Doug Stafford, about Perry's op-ed, he wrote in an e-mail“Utter nonsense. Interesting to be lectured entirely in talking points though. His new glasses apparently don’t make him see the world any more clearly."

Perry discussed his op-ed again on the Sunday shows this morning, where he made a few appearances to discuss border policy.

"The idea that I'm for opening up the gates and sending, you know, multiple numbers of American troops back into harm's way, is a bit of a stretch," he said on CBS's Face the Nation. "We need a strategy that is sound; we need a strategy that when we say we're going to do something, we do it. And our allies, again, can trust and our enemies fear us."

In case you've forgotten, Perry and Paul might also be thinking about presidential bids in 2016, hence they are feeling out Americans' views to decide which foreign policy platform suits them best. McCain wasn't interested in acting as an arbiter.

"So I'm not particularly interested in getting between Senator Paul and Governor Perry, but I do believe that the things we're seeing in the world today, in greater turmoil than at any time in my lifetime, is a direct result of an absence of American leadership," he said. "And we are paying a very, very heavy price now, and we will in the future, until we decide to understand that America has an essential role in maintaining peace and stability throughout the world, and that does not mean sending combat troops everywhere."

And so the battle over Republican foreign policy continues for at least one more Sunday.