Last week, the GOP’s savviest foreign policy expert in the Senate, Tennessee’s Bob Corker, announced he won’t run for re-election in 2018.

No doubt Corker knew he’d be primaried by pro-Trump populists who have declared war on mainstream Republicans. But this sober senator had probably tired of chairing the once-powerful Senate Foreign Relations Committee in the Trump era. Why hold serious hearings on weighty issues when they’ll be ignored by a president who makes foreign policy by Twitter?

Corker’s decision is one more reminder of the dangerous foreign policy confusion that has emerged under the Trump administration. And, apart from North Korea, there’s nowhere that confusion is more risky than in Trump’s contradictory policies toward the Middle East.

To be fair, any president would have had a tough time with the Mideast mess Trump inherited, the combined product of mistakes by Presidents Bush 43 and Obama along with the chaos of the Arab Spring.

And on the surface, Trump would seem to have returned to a traditional Republican approach to the Mideast: unremitting support for our Sunni Arab allies in the Persian Gulf and Israel, while working to curb Iranian mischief. Add to that “bomb the hell” out of the Islamic State and make the deal of the century on Israel-Palestine.

But the president’s own lack of discipline and disdain for process have turned his would-be Mideast policy into hash.

Point One. On the Sunni Arab alliance, the president was so entranced by the lavish reception he received from the Saudi royal family that he publicly endorsed its side in a quarrel with Qatar. Thus, Trump helped split the Sunni alliance and distracted its members from a coherent stance toward Iran.

Point Two. Stabilizing Iraq and Syria in the post-Islamic State era requires skilled American diplomacy with full presidential backing — or else the Islamic State 2.0 will emerge.

However, Trump’s military-only focus and indifference to broad long-term strategy offer little hope that proactive diplomacy will be on offer.

Which leads to Point Three. The United States needs to be talking seriously to Russia about how to stabilize post-Islamic State Syria lest it become another subsidiary of Iran. Shiite militias run by Iran now have access to the Syria-Israel border.

But Trump has made U.S. dialogue with Moscow impossible by his stubborn refusal to criticize Vladimir Putin or Russia’s interference in the 2016 elections. This makes even necessary dialogue with the Russians suspect.

Point Four. Trump seems to view his foreign policy as a solo operation .Moreover, he appears indifferent to the fact that Secretary of State Rex Tillerson is gutting the State Department, leaving few confirmed senior staff to ensure that policy is carried out.

Point Five. Under Trump, foreign policy is a family operation. He appointed his son-in-law, Jared Kushner, and a personal lawyer as the gurus supposed to bring peace to Israel and the Palestinians. This is a farce that is going nowhere.

Point Six. Most unnerving, the president’s strategic blindness threatens to put the Iranian ayatollahs back on a short-term path to a bomb.

Trump is reportedly about to refuse to certify that Iran is in compliance with the deal that sharply curtails their nuclear program.

America’s top military chiefs, along with Tillerson, say Iran is in compliance. The five other participants in the deal, Britain, France, Germany, Russia, and China, oppose Trump’s stance and would refuse to lift their sanctions. Corker, although an Iran hawk, has said Trump shouldn’t “tear up” the deal.

If he does, Washington would be left as the outlier and Iran would have the option to restart its nuclear program.

No wonder Corker is planning to retire.

Trudy Rubin is a columnist and editorial-board member for the Philadelphia Inquirer.