Tillerson's relationship with Trump fraught from the start

Tillerson and Trump clashed on almost every big foreign policy issue they faced.

But one of their most contentious moments came early in the administration when they clashed over the administration's approach to the Obama-era nuclear deal with Iran. During a meeting at the White House last summer the president became irritated with Tillerson after he encouraged him to certify the Iran deal and failed to present options for walking away from it.

"Rex and I have been talking about this for a long time," Trump said of his decision as he was departing the White House Tuesday. "We got along actually quite well, but we disagreed on things. When you look at the Iran deal, I thought it was terrible. He thought it was okay. I wanted to either break it or do something. He felt a little differently. So, we were not really thinking the same."

Tillerson was open about some of their disagreements as well. He told reporters in August after that meeting that Trump "and I have differences of views on things like JCPOA and how we should use it," using an acronym for the deal's formal name, the Joint Comprehensive Plan of Action.

To Tillerson, those differences were a sign of how he served Trump, of their "very open relationship, and it’s one in which I feel quite comfortable telling him my views."

But in addition to angering Trump, the fact that their disagreements were so public also undermined his ability to speak for Trump abroad, with foreign diplomats often questioning whether or not the nation's top diplomat spoke for his boss.

More often, Trump has stuck to his views, and the disagreements have soured their relationship. While Tillerson has worked with European allies to keep the deal in place and negotiate an add-on that combats Iran's "malign" behavior in the region and sanctions its ballistic missile program, Trump still desires to tear up the agreement that Obama's team negotiated.

Trump's decision to move the U.S. Embassy to Jerusalem was also opposed by Tillerson, who warned of security concerns and the damage it would do to the peace process and with Arab allies. Trump went ahead anyway.

Just last week, as Tillerson was pushing back on the perception that Trump does not care about Africa after his "s---hole" countries remark, Trump was implementing new tariffs on steel and aluminum - a move which Tillerson was against.