Tennessee Senator Bob Corker has unleashed a blistering attack on US President Donald Trump, after the two Republicans traded insults on Twitter.
Mr Corker accused the president of lying in a series of television interviews, adding that he debased the US and weakened its global standing.
Mr Trump fired back on Twitter, calling the top Senator a "lightweight" who "couldn't get re-elected".
The two men are due to meet at a Senate luncheon later on Tuesday.
Mr Trump's visit to Capitol Hill comes as the White House attempts to forge a consensus on the Republican tax reform plan.
"He is purposely breaking down relationships we have around the world that had been useful to our nation," Mr Corker said on CNN after Mr Trump published three critical tweets.
"Bob Corker, who helped President O give us the bad Iran Deal & couldn't get elected dog catcher in Tennessee, is now fighting Tax Cuts..." Mr Trump tweeted.
"I think the debasement of our nation is what he'll be remembered most for," the influential senator added.