WASHINGTON (NEXSTAR) — Some lawmakers are concerned about a possible resurgence of ISIS after President Donald Trump withdrew U.S. troops from Northern Syria last month.

Senator Bob Casey, D-Pennsylvania, said leaving America’s Kurdish allies vulnerable to attacks by Turkey was a bad decision that allowed hundreds of ISIS fighters to escape.

“It’s more likely now that ISIS will threaten American lives than it was before this decision,” he said. “What they got from President Trump was a total pulling the rug out from under them abandoning them and basically saying to President Erdogan from Turkey: You do whatever the hell you want.”

Casey said Trump’s main goal must be to confront and defeat ISIS.

“We’re hearing from the president that his only concern in the Middle East basically is oil,” Casey said.

Senate Democratic Leader Chuck Schumer, D-New York, recently introduced a bill that would require the creation of a plan to stabilize the region and prevent ISIS from becoming a greater threat.

“The president has chosen to welcome Erdogan to American soil before explaining to Congress his plan to defeat ISIS,” Schumer said. “How many ISIS members have been accounted for in the wake of our withdrawal?”

Senate Republicans blocked Schumer’s bill, with some lawmakers saying the unrest in that region dates back to the last administration.

“I think we all would like to see what the strategy or lack of strategy was from the last administration was that put us in this position,” Senator Rick Scott, R-Florida, said.

Congress hasn’t received a plan from Trump on ISIS yet, but Chairman of the Joint Chiefs of Staff Mark Milley said hundreds of U.S. troops will remain in other parts of Syria to counter ISIS in the meantime.