US veterans in Congress sounded off in protest to President Donald Trump's decision to condone an anticipated Turkish assault against the US-supported Kurdish militia in northeastern Syria.

The decision was made public late Sunday and forces roughly 1,000 US troops to step aside as Turkey prepares an offensive against the Kurdish-majority Syrian Democratic Forces near its border.

"Last night's announcement that the United States would be abandoning the Kurds is another stark reminder that 'American First' means 'America Alone,'" Democratic Rep. Ruben Gallego of Arizona, an enlisted Marine Corps veteran who served in Iraq, said in a statement.

"President Trump attacks the very people and relationships most needed to ensure our security. He throws his own people under the bus — even his Defense Department, who were reportedly blindsighted by the announcement. The President eats his own."

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US military veterans in Congress sounded off in protest to President Donald Trump's decision to condone an anticipated Turkish assault against the US-supported Kurdish militia in northeastern Syria.

The decision was made public late Sunday and forces roughly 1,000 US troops to step aside as Turkey prepares an offensive against the Kurdish-majority Syrian Democratic Forces near its border.

"Last night's announcement that the United States would be abandoning the Kurds is another stark reminder that 'American First' means 'America Alone,'" Democratic Rep. Ruben Gallego of Arizona, an enlisted Marine Corps veteran who served in Iraq, said in a statement. "President Trump attacks the very people and relationships most needed to ensure our security. He throws his own people under the bus — even his Defense Department, who were reportedly blindsighted by the announcement. The President eats his own."

"I urge the President to reconsider and take steps to ensure that our Kurdish allies remain safe," he added.

Read more: 'You remain a frickin' coward': Trump taunting a 2020 Democratic candidate and retired Marine isn't a laughing matter for some veterans

Turkey claims that the Kurdish People's Protection Units (YPG) and the SDF, are a threat with links to the Kurdistan Workers' Party (PKK), a US-designated terrorist group operating in its country. Kurdish troops, however, have led the ISIS fight on the ground in Syria and northern Iraq. The tenuous relationship has been evident as US forces struggled to establish a "safe zone" buffer in northern Syria between the Kurds and Turkey.

Trump, who previously sympathized with the Kurdish people, described them as "great people" and that he wanted to help the displaced group.

"They fought with us, they died with us," Trump said in a press conference last year. "We lost tens of thousands of Kurds fighting ISIS. They died for us and with us."

"We don't forget, I don't forget," Trump added at the time.

But following a phone call with Turkey President Recep Tayyip Erdogan on Sunday, Trump reversed course by proclaiming on Twitter that it was "time for others in the region ... to protect their own territory."

President Donald Trump speaks to Air Force personnel during an event September 15, 2017 at Joint Base Andrews in Maryland. Alex Wong/Getty Images

Read more: 7 Democratic lawmakers who served in the military and intelligence agencies accuse Trump of 'flagrant disregard for the law'

Other military veterans claimed Trump's comments were expectedly hollow.

"'We've got your back,' these are words every American veteran knows, we say that to one another, and we say it to our allies," Democratic Rep. Seth Moulton of Massachusetts, a retired Marine Corps officer who served in Iraq, said in a statement. "But Trump says it to our enemies: Putin, Assad and Kim Jong-Un."

"Now he's giving up our Kurdish allies — who've been some of the toughest fighters in Iraq for three decades —because an authoritarian Turkish president, more aligned with Russia than US allies, asked him for a favor," Moulton added.

Republicans who have served in the military also eschewed Trump and claimed the decision was "shortsighted and irresponsible."

"This to me is just unnerving to its core," Republican Sen. Lindsey Graham of South Carolina, a retired Air Force officer, said on Fox News.

Graham added that the move would ultimately hamper the fight against the Islamic State and reassure "the reemergence of ISIS."

Kurdish forces who have detained roughly 10,000 ISIS militants in makeshift prisons are expected to abandon their posts for the looming battle. The ISIS prisoners, which include foreigners whose host nations are reluctant to readmit them, will be taken into custody by Turkey, the White House said without specifics on Sunday.