Sens. Susan Collins Susan Margaret CollinsDemocratic senator to party: 'A little message discipline wouldn't kill us' Poll: 57 percent of Americans think next president, Senate should fill Ginsburg vacancy On The Trail: Making sense of this week's polling tsunami MORE (R-Maine) and Mark Warner Mark Robert WarnerFBI director casts doubt on concerns over mail-in voting fraud Democrats call for declassifying election threats after briefing by Trump officials It's time to upgrade benefits MORE (D-Va.) wrote to the Trump administration Tuesday demanding an assessment of the threat ISIS poses to the U.S. amid reports that several detained members of the terrorist group escaped captivity in northeastern Syria.

Collins and Warner, who both serve on the Senate Intelligence Committee, wrote a letter to acting Director of National Intelligence Joseph Maguire Joseph MaguireCongressional Democrats request FBI briefing on foreign election interference efforts Wells Fargo told employees to delete TikTok from work phones Hillicon Valley: Pompeo floats TikTok ban | Civil rights groups slam Facebook after call | Election security funding included in proposal MORE expressing “grave concern” over the escape of “several” ISIS detainees from detention facilities run by Kurdish groups that are currently embroiled in a standoff with Turkish forces in the area.

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“As the Kurds understandably shift their focus to defending themselves, their ability to securely detain these ISIS fighters will become increasingly uncertain. Already, press reports have indicated that senior U.S. officials say they have ‘no real idea’ how many fighters may have already escaped, and how many more are likely to do so,” the lawmakers wrote.

“Therefore, please provide to the Senate Select Committee on Intelligence an assessment of the impact the escape of ISIS detainees in SDF custody could have on the security of United States and our allies, including the detainees who have escaped and those still residing in SDF custody.”

The senators requested that the assessment from Maguire be delivered by Nov. 19 and be as “unclassified to the extent possible, with a classified annex if needed.”

The letter comes as bipartisan lawmakers continue to express concerns over the Turkish offensive in northeastern Syria, which critics of President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE say was green-lighted when the administration announced it would withdraw troops from the region. Many in Congress, including some traditional Trump allies, have worried that the retreat abandoned U.S.-allied Kurdish forces and could empower ISIS.

“Many of these individuals are hard-core terrorists, with the kinds of expertise — bomb-making, leadership and propaganda — that had made ISIS such a threat to the United States and our allies,” Warner and Collins wrote, referring to the estimated 10,000 captured ISIS fighters.

“If left unchecked, the escape of ISIS detainees in Syria could lead to similar counterterrorism setbacks,” they added, referring to the rise of ISIS that was fueled by al Qaeda prisoners who had broken out of detention.