Tucker Carlson, in characteristically nationalist language, endorsed the course of action as well, asserting on his Fox News show Monday night that the “apoplectic” reaction in Washington had cast into relief the bipartisan neoconservative consensus that prizes waging war above all else:

Of countless decisions Donald Trump has announced via Twitter, you’d think this would be the least controversial of all. … For once, Americans are coming home from a Middle Eastern tar pit, rather than staying forever, and we ought to be celebrating that.

Even some of the president’s critics lamented statements of disapproval from both House Speaker Nancy Pelosi and the Senate majority leader, Mitch McConnell. Emma Ashford, a research fellow at the libertarian-leaning Cato Institute, tweeted:

The most depressing part of this administration: Trump’s willingness to consider dialing down America’s military interventions is routinely met with more bipartisan criticism than his violation of constitutional norms or the rule of law.

Trump’s withdrawal is a betrayal

Many at home and abroad have condemned Mr. Trump’s decision as a cruel abandonment of faithful allies in need. As Ben Hubbard reported for The Times, the prospect of a Turkish military invasion has sparked a sense of both deep fear and indignation among Syrian Kurds.

“There were assurances from the United States of America that it would not allow any Turkish military operations against the region,” the Syrian Democratic Forces spokesman, Kino Gabriel, said in a television interview, adding that the “statement today was a surprise and we can say that it is a stab in the back for the S.D.F.”

The Syrian Democratic Coalition, the political wing of the S.D.F., said in a statement:

Our brave men and women with the Syrian Democratic ­Forces have just won a historic victory over the ISIS “caliphate,” a victory announced by President Trump and celebrated across the world. To abandon us now would be tragic.

In the United States, people across the political spectrum joined Lindsey Graham in sharing the S.D.F.’s sentiment. “What the U.S. just did in quitting Northern Syria and abandoning one of our strongest allies the Kurds sends a chilling message to would-be allies around the world,” the conservative commentator S.E. Cupp said. “Don’t bother committing to us, because we aren’t committed to you.”

Senator Chris Murphy of Connecticut tweeted along similar lines: