Rutgers professor Ross Baker was vacationing in Spruce Head, a tiny village on Maine’s Penobscot Bay, when word reached him that President Donald Trump was attacking Senate Majority Leader Mitch McConnell on Twitter.

Can you believe that Mitch McConnell, who has screamed Repeal & Replace for 7 years, couldn't get it done. Must Repeal & Replace ObamaCare! — Donald J. Trump (@realDonaldTrump) August 10, 2017

Mitch, get back to work and put Repeal & Replace, Tax Reform & Cuts and a great Infrastructure Bill on my desk for signing. You can do it! — Donald J. Trump (@realDonaldTrump) August 10, 2017

It was a stunning attack by Trump on the single most important legislator for kickstarting his stalled agenda, and it all stemmed from the news that McConnell had said in a low-profile speech Monday in Kentucky, “Our new president, of course, has not been in this line of work before. I think he had excessive expectations about how quickly things happen in the democratic process.” In Washington, Trump’s broadside left Republicans bewildered. “This makes about as much sense as sidelining Tom Brady because you didn’t like his answer at a news conference,” a senior GOP aide told Politico. “The reality is both men need each other to succeed.”

Baker, whose books on Congress include Friend & Foe in the U.S. Senate, racked his brain: Had a president ever been so openly critical of his party’s Senate leader?

“Without actually making a detailed search, certainly in terms of the openness and highly critical nature of the remarks, this is without precedent in modern times,” Baker told me. He marveled at the “real acerbity” of Trump’s tweet. “It’s really quite, quite pointed,” he said.

And yet, not completely unexpected either.