GOP allies blasted President Trump's decision to withdraw U.S. forces from northern Syria, condemning his decision to tacitly allow Turkey to mount an offensive against U.S.-allied Kurdish fighters in the region.

Why it matters: The split once again highlights how Trump's foreign policy impulses are often at odds with GOP orthodoxy — a trend that manifested just last week when Trump congratulated China on its 70th anniversary.

The big picture: Trump has pledged to reduce the U.S. military footprint around the world — controversially pondering a complete pullout from Afghanistan by 2020 — and the Syria decision is another part of that trend.

The U.S. had been trying for months to broker a truce between Turkey and the Kurds after the defeat of the Islamic State, or ISIS.

Former national security adviser John Bolton insisted months ago that the U.S. drawdown would need a Turkish agreement to protect the Kurds. Turkey bristled at that — and Bolton is no longer in his job.

What they're saying:

Senate Majority Leader Mitch McConnell (Ky.): "A precipitous withdrawal of U.S. forces from Syria would only benefit Russia, Iran, and the Assad regime. And it would increase the risk that ISIS and other terrorist groups regroup. ... American interests are best served by leadership, not by retreat or withdrawal," he wrote in a statement.

"A precipitous withdrawal of U.S. forces from Syria would only benefit Russia, Iran, and the Assad regime. And it would increase the risk that ISIS and other terrorist groups regroup. ... American interests are best served by leadership, not by retreat or withdrawal," he wrote in a statement. Sen. Lindsey Graham (S.C.): "This impulsive decision by the president has undone all the gains we've made, thrown the region into further chaos. ... I hope I'm making myself clear how shortsighted and irresponsible this decision is in my view. ... This to me is just unnerving to its core," he told "Fox & Friends."

"This impulsive decision by the president has undone all the gains we've made, thrown the region into further chaos. ... I hope I'm making myself clear how shortsighted and irresponsible this decision is in my view. ... This to me is just unnerving to its core," he told "Fox & Friends." Sen. Mitt Romney (Utah): "The President’s decision to abandon our Kurd allies in the face of an assault by Turkey is a betrayal. It says that America is an unreliable ally; it facilitates ISIS resurgence; and it presages another humanitarian disaster," he tweeted.

"The President’s decision to abandon our Kurd allies in the face of an assault by Turkey is a betrayal. It says that America is an unreliable ally; it facilitates ISIS resurgence; and it presages another humanitarian disaster," he tweeted. Sen. Marco Rubio (Fla.): He called the decision "a grave mistake that will have implications far beyond Syria."

He called the decision "a grave mistake that will have implications far beyond Syria." House Minority Leader Kevin McCarthy (Calif.): "I want to make sure we keep our word for those who fight with us and help us. If you make a commitment and somebody is fighting with you, America should keep their word," he told "Fox & Friends." Host Brian Kilmeade urged McCarthy to "call the president before it's too late."

"I want to make sure we keep our word for those who fight with us and help us. If you make a commitment and somebody is fighting with you, America should keep their word," he told "Fox & Friends." Host Brian Kilmeade urged McCarthy to "call the president before it's too late." Former UN Ambassador Nikki Haley: "We must always have the backs of our allies, if we expect them to have our back. The Kurds were instrumental in our successful fight against ISIS in Syria. Leaving them to die is a big mistake," she tweeted.

"We must always have the backs of our allies, if we expect them to have our back. The Kurds were instrumental in our successful fight against ISIS in Syria. Leaving them to die is a big mistake," she tweeted. Former Arkansas Gov. Mike Huckabee: "I generally support @POTUS on foreign policy & don't want our troops fighting other nations' wars, but a HUGE mistake to abandon Kurds. They've never asked us to do THEIR fighting — just give them tools to defend themselves. They have been faithful allies. We CANNOT abandon them," he tweeted.

"I generally support @POTUS on foreign policy & don't want our troops fighting other nations' wars, but a HUGE mistake to abandon Kurds. They've never asked us to do THEIR fighting — just give them tools to defend themselves. They have been faithful allies. We CANNOT abandon them," he tweeted. GOP House Conference Chair Liz Cheney (Wyo.): She called the decision "a catastrophic mistake," adding, "This decision ignores lesson of 9/11. Terrorists thousands of miles away can and will use their safe-havens to launch attacks against America."

She called the decision "a catastrophic mistake," adding, "This decision ignores lesson of 9/11. Terrorists thousands of miles away can and will use their safe-havens to launch attacks against America." Former Islamic State envoy Brett McGurk: "Donald Trump is not a Commander-in-Chief. He makes impulsive decisions with no knowledge or deliberation. He sends military personnel into harm’s way with no backing. He blusters and then leaves our allies exposed when adversaries call his bluff or he confronts a hard phone call," he tweeted.

The other side: Trump defended his decision in a lengthy tweetstorm on Monday morning, saying, "I held off this fight for almost 3 years, but it is time for us to get out of these ridiculous Endless Wars, many of them tribal, and bring our soldiers home. WE WILL FIGHT WHERE IT IS TO OUR BENEFIT, AND ONLY FIGHT TO WIN."

Go deeper: U.S. begins to withdraw troops from northern Syria after Trump's Turkey call