Tillerson held the brake on Trump's worst instincts. Now what? | Trudy Rubin

Rex Tillerson's biggest mistake was that he didn't retire with dignity on his own terms before his boss unceremoniously sacked him and named CIA chief Mike Pompeo as his successor.

The crude way it was done – Tillerson only learned of his firing via a presidential tweet – confirms that President Trump loves to reprise his role as star of The Apprentice.

But, of course, the bigger issue is what the switch will mean for an erratic foreign policy at a time when Trump faces critical decisions about the Iran nuclear deal, Russian aggression, and a possible summit with North Korea's leader.

Tillerson's close relationship with Defense Secretary James Mattis appeared to act as a brake on some of Trump's most bellicose instincts. The big question now: Has that brake been removed?

Of course, the president often displayed disdain for his then-secretary of state, contradicting him and not consulting him on key decisions. Foreign governments understood that Tillerson didn't have the president's ear, and the secretary's exit was long expected. Not to mention that Tillerson had gone far toward wrecking his own department, working in isolation while failing to defend its budget or top staff, who have left in droves.

But Tillerson persevered in presenting the president with differing opinions. "We disagreed on things," Trump said of the former oil executive. "With Mike Pompeo, we have a very similar thought process."

That "similar thought process" means former GOP congressman Pompeo will probably become a "yes man" to the president. Nowhere is that more worrying than on the nuclear agreement with Iran, at a time when the president is mulling whether to yank the United States out of the deal.

On Tuesday, Trump cited Iran as an issue on which he differed sharply with Tillerson: "When you look at the Iran deal, I think it's terrible. I guess he [Tillerson] thought it was OK.  I wanted to either break it or do something."

Tillerson repeatedly advised the president not to rip up the deal.  In this, he was correct. Walking away from this pact, at a time when Trump is seeking a nuclear accord with North Korea, would be senseless.

Leaving Iran free to resume nuclear development at a time when its behavior threatens Arab neighbors and Israel would be worse than senseless. All the more so when Trump has failed to develop any coherent policy toward Iranian advances in Syria and Lebanon.

Abrogating the deal could put Israel on a certain path to war with a nuclear-armed Iran, dragging the United States along.

Instead, Tillerson's State Department was leading talks with Britain, France, and Germany in an effort to forge a common front on pressing Iran to change the terms of the deal — or forge a follow-on pact to end Iran's ballistic missile testing and make the limits on Iran's nuclear program permanent.

Pompeo, on the other hand, declared just after the 2016 election: "I look forward to rolling back this disastrous deal with the world's largest state sponsor of terrorism."  His stance could confirm Trump's worst instincts on Iran.

Then there is Russia. Tillerson was willing to call out Russia for election interference and other aggressive behavior. Just this week, he attributed the poisoning of an ex-Russian spy in Britain to Russia and said it would "certainly trigger a response."

Pompeo has concurred that "Russians" [not Vladimir Putin] attempted to interfere in the 2016 election and will likely do so again in 2018.  But he has consistently downplayed the importance of the attacks. "It's true, yeah, of course," he said, but added, "They've been at this a hell of a long time. And I don't think they have any intention of backing off."

If Pompeo continues to display such diffidence about Russia's cyber attacks, he will bolster Trump's refusal to order a strong U.S. government response.

And finally, North Korea.  Tillerson long advocated back-channel diplomacy with Pyongyang and was publicly chastised by Trump for so doing.  The one-on-one meeting with Kim Jong Un, even if it comes off, won't produce a magic deal, but will require long follow-up talks — which Trump says he opposes.

Moreover, Kim is not going to give up his nuclear program, so any deal would have to revolve around limiting his program and ending nuclear and missile testing – a stronger version of the Iran deal.  Both Trump and Pompeo insist this would be a nonstarter.

So the arrival of Pompeo will likely bolster Trump's most hawkish instincts on Iran and North Korea as well as his strange reluctance to combat Russian machinations.  And it will probably undercut Mattis' leavening influence.

In the end, the only one to gain may be Tillerson himself, who was clearly unhappy in his post and seemed distraught in brief farewell remarks to journalists.

"I think Rex will be much happier now," Trump said. In that, he may be correct.

trubin@phillynews.com; @trudyrubin