MSNBC's Mika Brzezinski refuses to let squirming GOP senator off the hook on Trump's lies

Sen. Mike Lee (R-UT) tried to downplay the stunning criticism of President Donald Trump by two senators from the party they share -- but MSNBC's Mika Brzezinksi refused to let him off the hook.

The Republican senator, who did not endorse Trump's presidential campaign, insisted there was nothing unusual about Sen. Jeff Flake (R-AZ) denouncing the president from the Senate floor or Sen. Bob Corker's (R-TN) ongoing feud with Trump.

"Not every Republican agrees on every issue, not every Republican president agrees, either, with other Republican senators or with the president of the United States in every instance," Lee said, as Brzezinski cocked her head.

The Tea Party senator said the GOP was still committed to limited government and constitutional principles, and he would support Trump's efforts to preserve those principles.

"Are you seeing evidence of that?" Brezinski asked, and reminded Lee that Flake had accused the president of lying and personally maligning lawmakers.

Lee said he understood those concerns, but then fell back on political platitudes.

"The fact is, the president is there to do a particular job," Lee said. "The president has, in fact, fought to drain the swamp ... What I'm here to do is to fight for America's working families, America's moms and dads, and to make sure they get the tax reform and the regulatory relief they need and deserve."

Brzezinski reminded the senator that Trump had personally attacked Corker on Twitter with a demonstrably false claim, which Lee agreed he didn't like, and the "Morning Joe" co-host tried to pin him down.

"It's more than that, he attacked your colleague and lied about him," she said. "Isn't that where you step up and say, 'No, sir, I can't have this happening to my colleague?'"

Lee said the president and Corker should work out their disagreement themselves.

"You think this is between Sen. Bob Corker and the president, and this isn't a big problem?" Brzezinski said. "Because I could branch it out to a couple other lies to completely unhinged, unpredictable behavior by the head of your party that I think some might argue is damaging your party and is making a farce of conservatism."

The senator again said he understood the concern, but said he was too busy to "chase every squirrel" -- and then Brzezinksi dropped the hammer.

"Does the president of the United States lie?" she said. "Has he ever lied?"

Brzezinski finally got an answer, sort of.

"I'm certain that he has, but my purpose to come here today is not to focus on those things," Lee said, before calling for bipartisan unity to undo regulations and reform the tax code.