Indeed, he had.
Trump repeatedly promised to pull out of the deal on the campaign trail and had made it a target from the time that Barack Obama first entered into it in 2015.
His exit from the agreement is another instance of the Trump paradox: The president who says more outlandish and untrue things than anyone who has ever occupied the office of the presidency is also extraordinarily determined to deliver on his big promises.
Trump often doesn't mean what he says, but when he says what he means watch out. The combined forces of international pressure, polite opinion, outraged New York Times editorials, resistant advisers and sheer inertia aren't an obstacle.
Many of Trump's loose promises in the campaign weren't remotely deliverable (he was never going to drop Bowe Bergdahl out of an airplane over Afghanistan with no parachute).
But on his signature pledges, he's been committed, usually more than anyone around him. He's been particularly stalwart on those promises that require blasting through entrenched conventional wisdom and elite resistance.
What was most remarkable about Trump's promise to recognize Jerusalem as the capital of Israel and move the US Embassy there wasn't that he said it every recent president made similar sounds but that he actually did it.
George W. Bush said in 2000 that "as soon as I take office I will begin the process of moving the US ambassador to the city that Israel has chosen as its capital." Bill Clinton said he supported "the principle" of moving the embassy there. Obama was more circumspect, although he said that "Jerusalem will remain the capital of Israel." On this, Trump was more a man of his word than all of his predecessors.
One line of criticism of Trump from the right is that he's just doing what any other Republican president would do (with lots of uniquely Trumpian baggage). But it's not at all clear that another GOP president, even if he was on record favoring these moves, would have pulled out of the Paris climate accord and withstood the howls about imperiling the planet; or ended DACA despite all the media pressure to keep it; or exited the Iran deal with the Europeans waging an intense lobbying campaign in its favor.
It wasn't simply that these decisions had opponents. Their opponents were overrepresented in (allegedly) sophisticated circles with disproportionate cultural clout. Even conservatives who disdain the elite feel this cultural pull. Whereas Trump, who has never been house-trained as a politician, is more immune to it. He might crave the approval of respectable opinion, but he's also perfectly content to outrage it.
So, he's following through where others might equivocate or back off.
Of course, Trump isn't scrupulous with his words. Even when he's being relatively rigorous, he piles superlatives on top of exaggeration in what the real-estate business calls, delicately, "puffery." He'll simply make up things to wound his adversaries, and he's not telling the truth about the Stormy Daniels controversy.
Yet he's taking seriously the most important things he told his voters he'd do if elected, a key element of his bond with his base. They aren't always within his power to deliver, especially anything involving Congress. It clearly drives him crazy that on his most famous (and unrealizable) promise, to build a wall and have Mexico pay for it, he can't even get some photogenic construction going.
When Trump was elected, it seemed he might be endlessly flexible and up for grabs. He certainly is willing to say anything at any time. But he hasn't shifted or shrunk from the core commitments that defined his candidacy. So far, "he said he would do this," has been a remarkably reliable guide to the Trump agenda.