Islamic extremists have successfully adapted to international efforts designed to defeat them, according to the top Democrat on the House Intelligence Committee, opening the door to a deadly new phase in the group's evolution.

“The reality is even the best intelligence will not stop a determined enemy that adapts to our defenses,” Rep. Adam Schiff Adam Bennett SchiffChris Matthews ripped for complimenting Trump's 'true presidential behavior' on Ginsburg Trump casts doubt on Ginsburg statement, wonders if it was written by Schiff, Pelosi or Schumer Top Democrats call for DOJ watchdog to probe Barr over possible 2020 election influence MORE (D-Calif.) said on “ABC’s This Week” on Sunday. “And ISIS has adapted.”

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The comments followed the Islamic State in Iraq and Syria's (ISIS) devastating killings of 129 people across Paris on Friday night.

The extremist group’s surprising success in carrying out the violence comes on the heels of successful bombings in Beirut a day before, as well as last month’s downing of a Russian plane in Egypt. ISIS claimed responsibility for both events, signaling that the group is dramatically expanding its scope beyond the narrow slice of the Middle East that it controls.

Similar attacks appear inevitable, Schiff said on Sunday, unless global efforts are successful to root out the group from the chaos created by the civil war in Syria.

“The implications are this is not just an intelligence failure; it's a failure also of a coalition campaign," he said, "because we have allowed ISIS to have sanctuary in Syria and Iraq, with too much time to plan and plot, too much resources to be directed against us.”

“We are a harder target, a harder target to reach, but we know that ISIS aspires to attack us here in the United States as well.”

Friday’s string of shootings and bombings in Paris has further vexed the Obama administration’s efforts to fight ISIS, and led to new scrutiny on the apparent failings of its strategy.

The comments from Schiff — a Democrat — calling for a more robust effort to dismantle the organization signal a growing bipartisan frustration with the current policy of airstrikes and support for rebels and neighboring governments fighting the group.

“We're going to have to further constrain its space,” Schiff said.