(CNN) Republican Rep. John Shimkus of Illinois is going further than many of his fellow GOP lawmakers in criticizing President Donald Trump's shift in Syria strategy, declaring he no longer supports Trump altogether because of the move.

Even as congressional Republicans largely stand behind the President as he faces an impeachment inquiry in the House, lawmakers from Trump's own party this week have joined Democrats in widely condemnation of his recent decision that enabled Turkey to launch an attack on Kurdish forces who fought alongside Americans to defeat ISIS.

Trump decided to reposition a small number of US troops in northern Syria, effectively giving the green light to the Turkish offensive against the Kurds who have long been the US partner in fighting ISIS in Syria.

In an interview with radio station KMOX, Shimkus, who is not seeking reelection in 2020, condemned Trump's decision.

"It's terrible. It's despicable," he said.

"I'm heartbroken. In fact, I called my chief of staff in DC and said, 'Pull my name off the I support Donald Trump list.' We have just stabbed our allies in the back," Shimkus added. "This has just shocked, embarrassed, and angered me."

"President Trump is a populist who wants to put Americans first and to the detriment of our allies and friends," he said. "Some people in this country like that. I do not."

In a statement on Thursday, Shimkus elaborated on the choice to withdraw his support from Trump: "While my votes will continue to support the President's domestic policy agenda, because of this terrible foreign policy decision I asked that my name be removed from his campaign's official list of supporters."

Since the President announced his decision on Sunday, members of Congress from both parties have called on Trump to reverse course and support the Kurds.

"News from Syria is sickening," House Republican conference chair Liz Cheney tweeted on Wednesday. "Turkish troops preparing to invade Syria from the north, Russian-backed forces from the south, ISIS fighters attacking Raqqa. Impossible to understand why @realDonaldTrump is leaving America's allies to be slaughtered and enabling the return of ISIS."

Live updates: Turkey launches military offensive in Syria

And Sen. Lindsey Graham, otherwise a close ally of the White House, has called the situation "a disaster in the making" and argued it could pave the way for the re-emergence of ISIS.

Graham has also called for bipartisan legislation to punish Turkey with sanctions alongside Democratic Sen. Chris Van Hollen.

Trump on Wednesday pushed back on Graham's criticism but left open the possibility of sanctions for Turkey if Turkish President Recep Tayyip Erdogan "doesn't do it in as humane a way as possible." He did not provide details on what would define as humane.

"I think Lindsey would like to stay there for the next 200 years and maybe add a couple a hundred thousand people every place," Trump said. "But I disagree with Lindsey on that."

"This is a bipartisan issue," said Democratic Rep. Ro Khanna of California, a member of the House Armed Services Committee, said when asked about a potential congressional response on MSNBC Wednesday morning. "If Turkey continues this action, I think everything is on the table, from suspending arms sales to suspending economic aid to even considering their status in NATO."

"It's going to begin, certainly, the debate in Congress, and hopefully there's a clear message to Erdogan if President Trump isn't sending it that Congress on a bipartisan basis is sending it — that they cannot go and slaughter the Kurds who were our allies in the war against ISIS," Khanna added.