Back in the middle school lunchroom:

WASHINGTON (AP) — In a furious exchange of tweets and counter-tweets, President Donald Trump said a Republican senator “couldn’t get elected dog catcher” while the senator fired back that Trump was “utterly untruthful.”

“#AlertTheDaycareStaff,” tweeted Sen. Bob Corker, an outspoken GOP critic of Trump.

The latest contretemps come ahead of Trump’s planned lunch with Republican senators on Capitol Hill, as Congress turns its focus to overhauling the nation’s tax code.

Early Tuesday, Corker said on NBC’s “Today” that the Republican-led Congress should set the course on taxes after Trump shot down at least one GOP idea on retirement plans on Monday.

Asked if Trump should leave well enough alone, Corker said, “I think that’s the best way for us to have success.”