Donald Trump just stepped up attack on Republican Senator Bob Corker

Mr Trump plans on traveling up to Capitol Hill today to ask for party unity on tax reform

Republican Senator Bob Corker is the latest target of Donald Trump's Twitter ire. (Chip Somodevilla/Getty Images)

Donald Trump has yet again taken to Twitter, this time to slam Senator Bob Corker, a fellow Republican, the same day he plans to ask for party unity on tax reform.

The President tweeted that Mr Corker, the chairman of the Senate Foreign Relations Committee, helped President Barack Obama with the “bad Iran deal”.

He also said the Senator “couldn’t get elected dog catcher” in his home state of Tennessee.

Mr Corker announced earlier this year that he will be retiring from politics before the next election in 2018 and Mr Trump tweeted that he made the decision based on the President’s decision not to endorse him.

The President said the Senator, once an early ally of the real estate magnate, is now “only negative on anything Trump”.

The Twitter exchange is just the latest round of publicly exchanged barbs between the Oval Office and Mr Corker.

In another appearance early this morning on NBC's "Today" show, Mr Corker advised the President to “leave well enough alone” on the ongoing tax reform debate.

“I think that’s the best way for us to have success,” said the Republican Senator.

He also went on CNN to say that he felt Mr Trump was "unable to rise to the occasion" as a leader and said that he will not support him in another bid for the Oval Office.

Mr Corker said he does not "know why [Mr Trump] lowers himself to such a low, low standard and debases our country in the way that he does, but he does."

Mincing no words the Tennesseean commented: "I think the debasing of our nation ... will be what he'll be remembered most for."

He had also previously said the White House was akin to an “adult day care centre,” implying Mr Trump is a child.

"I don’t make comments I haven’t thought about," he told ABC's "Good Morning America" in doubling down on the "day care" statement.

Specifically on foreign policy, the Mr Corker has criticised the President’s use of Twitter to inflame tensions with North Korea, referring to leader Kim Jong-un as “Rocket Man” repeatedly and posting in a way that could be determined as fatalistic towards the use of military action against the isolated nation developing its nuclear weapons programme.

"The president undermines our Secretary of State, raises tensions in the area by virtue of the tweets that he sends out, and I would just like 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," Mr Corker told ABC News.

Mr Trump responded in kind by referring to Mr Corker as “Liddle” and said the Senator “begged” him for an endorsement for the next election.

Mr Corker has not tweeted using his official account since 24 September.

The President has tweeted his displeasure with many other politicians as well - most notably Hillary Clinton, whom he has referred to as "Crooked Hillary" on numerous occasions. Other targets of his ire include Republican Senator John McCain, Mr Obama, the NFL, Gold Star families who have lost military loved ones in action, and Democrats.

Mr Trump is going up to Capitol Hill this afternoon to ask for party unity on the administration's tax reform proposal.