Donald Trump opened up with both barrels Tuesday on a Republican senator who spent the morning calling his foreign policy amateurish and dangerous.

And his target gave as good as he got.

The president's tweeted broadsides at Tennessee Sen. Bob Corker come as he heads to Capitol Hill to meet with Republicans about a pending tax bill.

'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,' Trump tweeted.

'Corker dropped out of the race in Tennesse[e] when I refused to endorse him, and now is only negative on anything Trump. Look at his record!'

'Isn't it sad that lightweight Senator Bob Corker, who couldn't get re-elected in the Great State of Tennessee, will now fight Tax Cuts plus!' Trump added later.

Corker won his 2012 Senate election easily with 65 per cent of the vote.

By mid-morning Corker was uncorking at Trump on CNN, saying that 'much of what he says is untrue. ... I don't know why he lowers himself to such a low, low standard.'

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President Trump unleashed a new attack on Sen. Bob Corker (left), saying Tuesday that the Tennessee Republican is standing in the way of tax cuts

Corker said that Trump should leave diplomacy 'to the professionals' and stop 'kneecapping' his top diplomat

Trump tweeted Monday that Corker, who has announced his retirement as of next year, 'couldn't get elected dog catcher in Tennessee

By mid-morning Corker was uncorking at Trump on CNN, saying that 'much of what he says is untrue. ... I don't know why he lowers himself to such a low, low standard'

Asked if he would support Donald Trump in the future, Corker said: 'Let's just put it this way, I would not do that again. No way. No way.'

'I think the debasement of our nation will be what he'll be remembered most for, and that's regretful,' he said, insisting that Trump is a poor role model for American children.

'We have young people who for the first time are watching a president stating, you know, absolute nontruths nonstop, personalizing things in the way that he does. It's very sad for our nation.'

Corker has minced no words about his disdain for Trump's approach to foreign policy, and said Tuesday morning on ABC that the president should stop 'kneecapping' his top diplomat.

And he insisted the president should abandon his scattershot approach to the North Korea nuclear crisis and leave it 'to the professionals for a while.'

Trump shoved back – hard.

'Sen. Corker is the incompetent head of the Foreign Relations Committee, & look how poorly the U.S. has done,' the president tweeted.

'He doesn't have a clue as the entire World WAS laughing and taking advantage of us. People like liddle' Bob Corker have set the U.S. way back. Now we move forward!'

The Tennessee senator was back to talking about 'day care staff' on Tuesday

Trump fired back less than an hour later

In remarks to reporters as the feud reached a fever pitch, House Speaker Paul Ryan said he hoped the Trump-Corker tensions would calm down over lunch.

'I'm glad the president's coming to lunch because I have long believed that it's best to settle these things in person and I hope they can get the chance to do that,' Ryan said.

Corker, who chairs the Senate Foreign Relations Committee, has already announced that he will not seek another term in office, opening the door for the kind of frank statements that are seldom heard from politicians preparing for re-election.

Trump publicly chided Secretary of State Rex Tillerson this month for being optimistic about a rapprochement with North Korean dictator Kim Jong-Un

By mid-morning, Trump was attacking Corker on substance, calling him an 'incompetent' Senate Foreign Relations Committee chairman

Corker's chief of staff Todd Womack insisted this month that his boss wasn't bowing out because of a lack of support from the White House.

'The president called Senator Corker ... and asked him to reconsider his decision not to seek re-election and reaffirmed that he would have endorsed him, as he has said many times,' Womack said on October 8.

'I want to support these efforts that are underway,' Corker said Tuesday, referring to Secretary of State Rex Tillerson's outreach designed to quietly bring North Korea's government to the bargaining table.

But 'the president undermines our secretary of State [and] raises tensions in the area by virtue of the tweets that he sends out,' Corker said on ABC's 'Good Morning America' program.

Sen. Corker unleashes on Trump in stone cold interview w/@mkraju, “[Trump] has great difficulty with the truth..." https://t.co/VAhVkQqxwP — Ashley Codianni (@AshleyCodianni) October 24, 2017

Corker smacked the president on Oct. 8, tweeting that the White House had 'become an adult day care center'

'And I would just like for him to leave it to the professionals for a while and see if we can do something that's constructive for our country, the region, and the world.'

Corker and Trump have been engaged in an online war of words this month – with the president claiming Corker failed to stop Barack Obama's nuclear deal with Iran, and Corker firing back that Trump's White House is an 'adult day care center.'

Responding to Trump's tweets on Tuesday, Corker wrote on Twitter: 'Same untruths from an utterly untruthful president. #AlertTheDaycareStaff'

He softened his language on television but left no doubt about his meaning.

'Really, when you look at the fact that we've got this issue in North Korea and the president continues to kneecap his diplomatic representative, the secretary of State, and really move him away from successful diplomatic negotiations with China, which is key to this, you’re taking us on a path to combat,' Corker said.

'It appears to be the governing model of this White House to purposely divide,' he added in an interview on CBS.