Washington: If President Trump hopes to step up pressure on Iran, he didn’t do his cause much of a favour this weekend by picking a fight with Republican Senator Bob Corker.

Trump’s ire was apparently drawn by comments Corker made last week in which he suggested that Secretary of State Rex Tillerson, Defence Secretary Jim Mattis and White House Chief of Staff John F. Kelly “are those people that help separate our country from chaos.”

It didn’t take much guesswork to figure out what — or who — he meant by “chaos.”

On Sunday morning, Trump responded with a trio of tweets alleging that Corker “begged” him for an endorsement in his 2018 reelection campaign and that Corker decided not to run — he announced that decision late last month — only because he did not “have the guts.”

Corker quickly responded with his own caustic message: “It’s a shame the White House has become an adult day care centre. Someone obviously missed their shift this morning.”

Hours later, Trump responded: “Bob Corker gave us the Iran Deal, & that’s about it. We need HealthCare, we need Tax Cuts/Reform, we need people that can get the job done!”

In the Trump era, Twitter feuds are a dime a dozen — but this one will have bigger consequences than most.

Corker, the chairman of the Senate Foreign Relations Committee, is a powerful voice when it comes to foreign policy. And while he was once a Trump ally — he advised Trump during last year’s campaign and was considered a contender for secretary of state — Trump’s in-office behaviour and Corker’s upcoming retirement have changed everything. Now Corker has nothing left to lose — and perhaps a whole lot to prove.

When it comes to Iran, this will be important. Trump has repeatedly criticised the 2015 agreement that limited Tehran’s nuclear activities, once dubbing it “the worst deal ever.”

This week, he is expected to announce a plan to “decertify” the agreement, claiming the deal is not in the interests of the United States. Congress would then have to decide whether to reinstall sanctions on Iran, a move that could collapse the agreement altogether.

However, as my WorldViews colleague Amanda Erickson has explained, the president’s plan is already a big compromise.

Trump could have unilaterally killed the deal by refusing to issue the waivers that kept the old sanctions from being imposed.

Instead, he punted the decision to Congress. The Post also reports that he may hold off on recommending that sanctions be reinstated.

For the White House, the hope seems to be that the threat of sanctions will make Congress agree to a renegotiation of the Iran deal.

In the resulting bipartisan debate about how to deal with Iran, the widely respected Corker would play a big role.

“If there is any Republican on Capitol Hill who stands a chance of persuading Democrats to come on board, it is Corker,” as The Post’s Karoun Demirjian put it Sunday.

Given the small Republican majority in the Senate, Trump needs Corker’s support for a number of other legislative measures, including tax reform and health care. Corker also controls diplomatic confirmations, which means he could hold up the appointment of a new secretary of state if Rex Tillerson — another man in questionable standing with Trump — leaves office.

That the president would get into an unnecessary spat with a man whose help he badly needs has confounded some critics. “Trump’s entire Iran plan rests on a careful dance with Congress,” Ilan Goldenberg, a former Obama administration official and the director of the Middle East Security Programme at the Centre for a New American Security, wrote on Twitter. “Corker may be the most important partner in that dance. This is so dumb.”

There may be some twisted method to Trump’s madness. He is aware that the majority of Americans, many of US allies and even a number of senior members of his own staff favour keeping the deal. He also knows his own base is deeply sceptical of the deal, and he is keen to undermine the Obama-era agreement if he can.

By handing off any real decision to Congress, he can avoid having to make a hard decision himself. And by picking a fight with Corker, he has a scapegoat if his supporters grow frustrated with a lack of action in Congress. It seems plausible that Trump’s allies are simply being prepared for another legislative failure.