Some of President Donald Trump’s staunchest allies aren’t on board with the White House’s abrupt Sunday night announcement that U.S. troops will begin withdrawing from Turkey’s border in northeastern Syria.

According to the New York Times, Trump’s decision to withdraw U.S.-backed Kurdish fighters — who have been instrumental in the U.S. fight against the Islamic State — in northeast Syria goes against senior leaders’ advice in his administration. The State Department and the Pentagon have advocated for a small presence in the region to fight ISIS, according to the Times.

In a statement Monday obtained by the Associated Press, Syrian Kurdish fighters accused Washington of abandoning them.

Trump defended the move Monday morning in a series of tweets:

The United States was supposed to be in Syria for 30 days, that was many years ago. We stayed and got deeper and deeper into battle with no aim in sight. When I arrived in Washington, ISIS was running rampant in the area. We quickly defeated 100% of the ISIS Caliphate,….. — Donald J. Trump (@realDonaldTrump) October 7, 2019

…..again said “NO,” thinking, as usual, that the U.S. is always the “sucker,” on NATO, on Trade, on everything. The Kurds fought with us, but were paid massive amounts of money and equipment to do so. They have been fighting Turkey for decades. I held off this fight for…. — Donald J. Trump (@realDonaldTrump) October 7, 2019

…figure the situation out, and what they want to do with the captured ISIS fighters in their “neighborhood.” They all hate ISIS, have been enemies for years. We are 7000 miles away and will crush ISIS again if they come anywhere near us! — Donald J. Trump (@realDonaldTrump) October 7, 2019

Trump’s unprecedented move sparked backlash Monday morning from his closest allies.

Senate Majority Leader Mitch McConnell said in a Monday afternoon statement that the move “would only benefit Russia, Iran, and the Assad regime.”

NEW: Mitch McConnell weighs in on Syria: `A precipitous withdrawal of U.S. forces from Syria would only benefit Russia, Iran, and the Assad regime,' he says. pic.twitter.com/YTmoA1A4dz — Laura Litvan (@LauraLitvan) October 7, 2019

“Fox & Friends” host Brian Kilmeade called the move a “disaster.”

“The reason our casualties were so low is because the Kurds did all the fighting,” Kilmeade said. “Now we’re saying ‘Okay Turks, go wipe them out. Or force them out.’ What kind of message is that to the next ally that wants to side with us?”

Watch Kilmeade’s reaction below:

"Fox & Friends" host Brian Kilmeade isn't happy with Trump's abrupt Syria pullout pic.twitter.com/fS6C4cVzwx — TPM Livewire (@TPMLiveWire) October 7, 2019

Trump’s closest allies in Congress also issued choice words in reaction to the move:

I don’t know all the details regarding President Trump’s decision in northern Syria. In process of setting up phone call with Secretary Pompeo. If press reports are accurate this is a disaster in the making. — Lindsey Graham (@LindseyGrahamSC) October 7, 2019

If reports about US retreat in #Syria are accurate, the Trump administration has made a grave mistake that will have implications far beyond Syria. — Marco Rubio (@marcorubio) October 7, 2019

Withdrawing US forces from Northern Syria is a catastrophic mistake that puts our gains against ISIS at risk and threatens US security. This decision ignores lesson of 9/11. Terrorists thousands of miles away can and will use their safe-havens to launch attacks against America. — Liz Cheney (@Liz_Cheney) October 7, 2019

Once again @realDonaldTrump uses Rand Paul’s “endless wars” talking points as he orders America to once again abandon our friends and give Russia & Iran exactly what they want. This is wrong. #Syria — Adam Kinzinger (@RepKinzinger) October 7, 2019

Strongly disagree with @POTUS Trump decision to allow Erdogan to invade Syria. Betrays Kurds, strengthens ISIS and endangers American homeland. — Rep. Pete King (@RepPeteKing) October 7, 2019

On Monday afternoon, Sen. Mitt Romney (R-UT) joined the GOP opposition to the Syria pullout in a joint statement with Sen. Chris Murphy (D-CT).

In stmt, Romney &Murphy say "Barring a reversal of this decision, the Admin must come before the Sen Foreign Relations Cmte & explain to the American people how betraying an ally & ceding influence to terrorists & adversaries is not disastrous for our national security interests" pic.twitter.com/7adrmViC0y — Frank Thorp V (@frankthorp) October 7, 2019

Some of Trump’s former Cabinet members joined in on the criticism as well, such as former UN Ambassador Nikki Haley and former ISIS envoy Brett McGurk:

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. #TurkeyIsNotOurFriend — Nikki Haley (@NikkiHaley) October 7, 2019