President Donald Trump's feud with a member of his own party erupted Tuesday, as the president delivered blow after blow on Twitter to Sen. Bob Corker, while the outgoing senator again warned about Trump's fitness to serve only hours before they both attended a Senate GOP policy lunch.
In tweets Tuesday, Trump contended the Tennessee Republican is "fighting" tax cuts and "couldn't get elected dog catcher." The president again claimed that Corker chose not to run for re-election when Trump "refused" to endorse him and said he "now is only negative on anything Trump."
Responding later in a CNN interview, Corker rebutted Trump and again took the remarkable step of questioning the president's fitness for office. The senator said "nothing" that Trump wrote in his tweets was truthful. He added that the president "debases our country" and will not "rise to the occasion as president."
Corker said he would not support Trump again and contended that the president has "great difficulty with the truth," part of an escalating feud that complicates the GOP's push to overhaul the American tax system.
Trump's latest spat with a senator in his own party comes only hours before he is set to have lunch with Republican senators and discuss tax policy, the main focus of the Republican agenda.
Corker responded to Trump's initial messages on Twitter, calling the charges the "same untruths from an utterly untruthful president." "Alert the day care staff," he added, pointing to his recent reference to the White House as an "adult day care center."
The day started with Corker telling NBC that he hoped the White House would "step aside" and let the Senate and House tax-writing committees carry out the normal process of crafting a tax bill.
"I think that's the best way for us to have success," he said of Trump staying out of the debate. He also called Trump's appearance at the lunch a "photo op."
Trump then made his tweets. He continued to hammer Corker in tweets throughout the day, calling the senator "incompetent" and saying he contributed to setting the U.S. "way back."
The latest back-and-forth between Trump and a top senator in his party threatens to throw a wrench in the GOP's push to pass a tax plan this year that chops rates for individuals and corporations. Corker had already expressed concerns about supporting a bill that would balloon the federal deficit.
The current GOP tax framework, though far from finalized, could seriously expand the deficit if Republicans do not add any revenue boosters.
The House could pass the Senate's version of a budget this week, a key step in the process. Then, tax-writing committees would work toward crafting a draft bill that they could release in the coming weeks.
The GOP has struggled to agree on provisions that could offset the tax cuts. On Monday, Trump said the Republican plan would not make changes to a popular retirement savings plan, ruling out one possible money-raising tool.
On Tuesday morning, Sen. Marco Rubio, R-Fla., told CNBC he believes that Corker will ultimately get behind the tax plan despite his reservations about the budget deficit and disagreements with Trump.
Republicans may need Corker's vote. With no Democratic support for the plan expected, the GOP is using the budget reconciliation process. The rules will require only 50 of 52 Republican senators to vote for the bill.
While Trump claims Corker is "fighting" tax cuts, he voted for the Senate budget plan that would help to unlock the reconciliation rules for a tax bill.