Delaware Sen. Christopher Coons Christopher (Chris) Andrew CoonsMurkowski: Supreme Court nominee should not be taken up before election Battle lines drawn on precedent in Supreme Court fight Sunday shows - Ruth Bader Ginsburg's death dominates MORE (D) on Sunday said President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE is "handing a great big Christmas gift" to Russia and Iran by withdrawing U.S. troops from Syria.

"And it’s a pretty clear guide post for me, when there’s a foreign policy decision that’s cheered by [Russian President] Vladimir Putin and [Republican Kentucky Sen.] Rand Paul Randal (Rand) Howard PaulRand Paul says he can't judge 'guilt or innocence' in Breonna Taylor case Overnight Health Care: Health officials tell public to trust in science | Despair at CDC under Trump influence | A new vaccine phase 3 trial starts Health officials tell public to trust in science MORE, that’s a pretty good sign it’s a terrible idea," Coons, a member of the Senate Foreign Relations Committee, added.

The White House last week announced it would withdraw U.S. forces from Syria, a move that was met with bipartisan backlash from lawmakers in Washington.

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Trump claimed he was removing the troops because the U.S. has defeated the Islamic State in Iraq and Syria (ISIS) in the region, but Coons warned Sunday that there is still work to be done.

“We shouldn’t fumble the ball on the 5-yard line. The mission against ISIS, where the United States built a coalition of dozens of countries, is on the verge of winning — of completely shutting down ISIS in Syria," Coons said.

"And for us to withdraw right now and abandon our Kurdish allies, paves a highway for control of Syria for either Iran and Russia or Turkey," he added.

The decision to withdraw from Syria also prompted the resignation of Defense Secretary James Mattis James Norman MattisBiden courts veterans amid fallout from Trump military controversies Trump says he wanted to take out Syria's Assad but Mattis opposed it Gary Cohn: 'I haven't made up my mind' on vote for president in November MORE, who wrote in his resignation letter that Trump has "the right to have a Secretary of Defense whose views are better aligned with yours."

Coons said Sunday that he would not support the nominee to replace Mattis if it's someone who "doesn't believe in the importance of our alliances" and doesn't "have a clear-eyed view" of threats posed by Russia and China.

"And they won’t enjoy the broad bipartisan support that Secretary Mattis has for so long," Coons added.