President Trump’s decision to order American forces to fire dozens of missiles at a Syrian air base — in retaliation for a chemical weapons attack that the U.S. believes was authorized by the government of Bashar al-Assad — was one of the most important acts of his presidency so far and, in some ways, one of the most surprising.

A defining feature of the early part of Trump’s tenure has been the consistency between his campaign rhetoric and his actions as president, including eliminating environmental regulations, trying to ban travelers from majority-Muslim countries and more aggressively enforcing immigration law. But Trump also campaigned as the “America First” president who would avoid inserting the nation into conflicts abroad.

“One day we’re bombing Libya and getting rid of a dictator to foster democracy for civilians, the next day we are watching the same civilians suffer while that country falls apart,” Trump said in a speech laying out his approach to foreign policy in April 2016. “We’re a humanitarian nation. But the legacy of the [former President Barack] Obama [and former Secretary of State Hillary] Clinton interventions will be weakness, confusion and disarray.”

After Mike Pence suggested in the vice presidential debate last fall that the U.S. should take a stronger stance against the Assad regime, Trump publicly dismissed this view, saying “Syria is fighting ISIS.” In an interview with the Guardian during the campaign, Trump said, “What we should do is focus on ISIS. We should not be focusing on Syria.”

He continued this rhetoric after his election, including as recently as earlier this week. “I’m not, and I don’t want to be, the president of the world,” he said at an event on Tuesday in Washington, as he was highlighting his opposition to free-trade agreements.

The airstrikes on Thursday are a break from his established stance and represent a more aggressive foreign policy. Perhaps circumstances changed and therefore so did Trump; it could be that Trump felt compelled to act because the use of chemical weapons crossed “many, many lines,” but that he will then immediately return to the national security approach he spoke of in 2015 and 2016, rendering this military response an outlier.

In his remarks on Thursday night, however, Trump cast the strikes as in keeping with an “America First” approach. He said, “it is in this vital national security interest of the United States to prevent and deter the spread and use of deadly chemical weapons,” and “the refugee crisis continues to deepen and the region continues to destabilize, threatening the United States and its allies.”

But despite this rhetorical framing, the bombing of the Syrian base was also a military action meant to help Syrians who aren’t aligned with Assad, a move with both humanitarian — “Beautiful babies were cruelly murdered,” the president said in remarks after the strikes — and interventionist overtones. Trump traditionally has not spoken of foreign policy in that way. And the action in some ways represented America acting as the world’s leader, its policeman, in contradiction to what Trump implied on Tuesday.

For more evidence that the airstrikes were a departure from Trump’s usual rhetoric, look no further than who he is agreeing with: Hillary Clinton. Clinton, speaking at an event in New York earlier on Thursday, had said that the U.S. should attack Syrian airfields. During the campaign, Trump had attacked Clinton as too eager to use military force abroad, constantly dismissing her views on world affairs. “You’re going to end up in World War Three over Syria if we listen to Hillary Clinton,” he said in October.

Trump’s decision, while surprising, was also significant for at least a few reasons. First, it was a break with the more cautious policy of Obama, who had considered launching airstrikes in Syria in retaliation for the use of chemical weapons but decided not to. Second, the Assad regime is closely aligned with Russia; Trump has been criticized for being too soft in his approach to Russia, but at least on this policy, Trump has taken a stand that is against Russian interests.

Third, Trump took military action unilaterally, without United Nations authorization, other nations joining in the strikes or formal approval from Congress. That could draw criticism from several directions. For example, Kentucky Sen. Rand Paul, a Republican, had said that Trump would need to get congressional authorization before attacking Syria.

It’s also not clear how the public will react to Trump’s decision. In 2013, a CBS News/New York Times poll found that a majority of Americans (57 percent) said that the U.S. should not launch airstrikes in Syria. A Gallup poll from last year showed that 34 percent of Americans wanted the U.S. more involved in Syria, but a majority said America should either remain at its current level of involvement (29 percent) or do less (30 percent). But both those polls were taken while Obama was in office; partisan views of Obama and Trump may affect how Americans feel about Syria policy, and the photos of children who were killed by the chemical weapons attack could shift public opinion as well.

Finally, authorizing military action and then addressing the nation is a big, presidential action, the kind Trump had not yet undertaken. It puts Trump at the center of the action, instead of reacting to Congress, and it complicates the strategy of Democrats, who generally oppose whatever this president proposes.

Trump’s policies tend to be either hated by Democrats and Republicans or hated by just Democrats. The early reactions to this military strike suggest that this policy may scramble the traditional partisan alignments, with some more libertarian Republicans opposing it and some former Obama aides backing it.

“Making sure Assad knows that when he commits such despicable atrocities he will pay a price is the right thing to do,” Senate Democratic leader Chuck Schumer said in a statement after the attack. “It is incumbent on the Trump administration to come up with a strategy and consult with Congress before implementing it.”

Schumer was both praising Trump (“right thing”) and criticizing him (“consult with Congress”). That was perhaps the most equivocal statement Schumer has given about Trump this year. At least in the short term, Trump and his opponents are both in new territory.