Donald J. Trump started the feud with John McCain.

The president vs. the senator is now getting serious. I’ll stipulate that I’m rooting for the senator who once was his party ‘s presidential nominee.

This intraparty feud could get in the way of some serious policy matters.

The president fired the first shot in the feud when he told an interview that he didn’t consider the Arizona Republican U.S. senator to be a war hero. Trump said McCain is a hero only because “he was captured. I like people who aren’t captured. OK?”

I was among those who thought that comment would doom Trump’s budding presidential candidacy. Silly me. I was so wrong!

McCain ever since has been none too bashful about criticizing Trump. McCain’s foreign policy credentials are well known. He believes Trump is too friendly with Russian strongman Vladimir Putin and has said so publicly.

The feud has taken a new turn. McCain has criticized a military mission that Trump ordered. Trump and his team have said McCain should apologize for impugning the memory of a Navy SEAL who died in the operation in Yemen.

From where I sit, I didn’t here McCain disparage the gallantry of the fallen commando. It would be unthinkable for the former Vietnam War prisoner to say such a thing.

But this war of words between the leading Republicans doesn’t bode well for the new president getting much through the GOP-led Congress. It’s not that McCain is terribly popular among his colleagues; the difficulty might lie in McCain’s well-chronicled service to the country, which is infinitely greater than any such service Trump ever performed before he was elected president.

The Hill reports: “Further fights between McCain and Trump seem almost certain. Neither likes to back down from a fight, and it is hard to believe that Trump’s criticisms of McCain haven’t got under his skin.”

I am quite certain as well that Trump’s famously thin skin is pretty chapped these days, too.