Sen. Bob Corker (R-Tenn.) admonished President Trump on Tuesday to stop interfering in the debate over tax legislation and said his volatility could lead the United States into war, prompting a slew of Twitter insults from the president and renewing a long-simmering feud just hours before he is scheduled to visit Capitol Hill.

"I would just like him to leave it to the professionals for a while and see if we can do something that's constructive," Corker said on ABC's Good Morning America, referring to the debate over restructuring the tax code. "If you start taking things off the table before you get started, you make it very difficult."

Trump, whose relationship with the senator has rapidly deteriorated in recent weeks, returned fire by insulting Corker on Twitter.

The feud lays bare tensions between Trump and congressional Republicans that are already complicating GOP efforts to advance tax cuts, the party's last-ditch attempt at a major policy accomplishment this year.

 Trump has promised changes to the tax code will not affect tax-deferred retirement plans, the mortgage interest deduction or the deduction for charitable contributions. Republicans like Corker, one of Trump's most vocal GOP critics, say these promises raise expectations prematurely while making it more difficult for lawmakers to make up the revenue lost to tax cuts.

The strained relations between the president and Republican senators, which go far beyond Trump's fight with Corker, add uncertainty to the GOP's effort to cut taxes and enact other policy priorities.

Trump has sharply criticized Senate Majority Leader Mitch McConnell (R-Ky.) for failing to repeal and replace the Affordable Care Act. Republican senators have also thrown some rhetorical elbows at the president.

Corker's pointed comments came just ahead of Trump's planned visit to the Senate to address Republicans at their weekly policy luncheon.

In a round of interviews, he stood by his previous description of the White House as an "adult day-care center" and his comment that Trump's volatility could set the United States on a "path to World War III."

"I don't make comments I haven't thought about," the senator said on Good Morning America.

"The president continues to kneecap his diplomatic representative, the secretary of state, and really move him away from successful diplomatic negotiations [related to North Korea] . . . You're taking us on a path to combat," said Corker, who is chairman of the Senate Foreign Relations Committee.

 Asked whether he regrets supporting Trump, Corker told CNN he would not do it again.

"The president has great difficulty with the truth on many issues," he said. "He's proven himself unable to rise to the occasion."

On Twitter, Trump attacked Corker for helping former President Barack Obama "give us the bad Iran Deal," and said Corker changed his plans to run for reelection in 2018 after Trump declined to endorse him.

In reality, Corker organized opposition to the Iran deal and voted against it. The senator and his top aide have said Trump offered his support for Corker's reelection, and that after Corker announced he would retire after next year, Trump called asking him to reconsider and to run again.

"Same untruths from an utterly untruthful president," Corker tweeted Tuesday. He added the hashtag #AlertTheDaycareStaff, repeating an earlier description of Trump's White House.

While GOP aides and senators predicted Monday that Trump's visit would center mostly on the effort to rewrite the nation's tax laws, the broad array of topics on their mind, coupled with the president's penchant for suddenly veering from one subject to another, could open the door to an unpredictable afternoon.

"I want him to tell us to do our job," said Sen. David Perdue (R-Ga.), a Trump ally who, like the president, has openly voiced his frustration that a handful of Republican senators sank the repeal-and-replace effort. He expected the president would argue that the tax- reform push is "bigger than tax," in that it marked a chance for Republicans to prove they can govern, among other things.

When Trump addresses the luncheon the Republican senators attend each Tuesday afternoon in a room near the Senate chamber, "it's important for him to convey to us the things that he thinks are priorities, and not only with respect to the tax bill, but some of the other things that we are currently working on," said Sen. John Thune (S.D.), the third-ranking Republican senator.

One of the other issues Republicans are wrestling with is health-care reform. Trump's decision to end federal subsidies to help offset lower-income Americans' coverage costs led a bipartisan coalition of senators to offer a compromise bill that would authorize those funds. In exchange, states would have broader leeway in regulating coverage under the ACA.

Trump, who phoned Democratic and Republican lawmakers this month to push them to make a deal, has sent mixed signals on the plan, seeming to support it before backing away.

White House officials are urging Senate Republicans to move the bill to the right, by including provisions offering retroactive relief from the ACA's insurance mandates for individuals and certain employers, according to people briefed on the talks.

"The White House has the ball right now," said Sen. Lamar Alexander (Tenn.), the Republican who took the lead on negotiating the bipartisan package. "They've made some suggestions publicly about what they'd like to see in the bill. I'm for all of those things. The question is whether they can persuade Democratic senators to agree to that."

But Alexander, who said that an analysis of his plan by the nonpartisan Congressional Budget Office could be released as early as Tuesday, wasn't expecting to hear Trump sketch out his latest thinking on the framework during lunch. In his view, that would be a good thing. "I'd like for the president to focus on tax reform," he said.

Others, however, were eager to hear Trump talk health care.

"I'd like to hear him reinforce the movement to get something done" on health care, said Sen. Mike Rounds (R-S.D.), who supports the deal Alexander reached with Sen. Patty Murray (D-Wash.).

Looming over the luncheon are the mutual hostilities between Trump and Republican senators. On Twitter and in remarks before television cameras, Trump has slammed McConnell and attacked other senators.

GOP senators have also landed their own blows. McConnell, for instance, has said that Trump's limited experience in politics created "excessive expectations" for passing landmark legislation.

Until Tuesday morning, both sides had appeared determined to move past their differences and project more harmony. Trump and McConnell sat down for lunch at the White House last Monday and came out for a 40-minute joint news conference afterward.