Matthew G. Olsen, another former director of the counterterrorism center, said the series of major attacks would compel the White House to take additional steps. “All of this raises the stakes for the U.S. and increases pressure on the U.S. and the West to respond more aggressively,” he said.

Escalating action against the Islamic State carries its own risks. The Russian airliner was attacked after Moscow intervened in Syria. And the Islamic State has warned it would step up strikes against those countries that have joined the American-led coalition fighting the group in Iraq and Syria.

“The operational tempo is increasing on both sides,” Mr. Olsen said. “We’re increasing our attacks in Syria and Iraq, and ISIS is increasing their attacks as well.”

Representative Adam B. Schiff of California, the ranking Democrat on the Intelligence Committee, said the attacks should dispel any illusions about the nature of the Islamic State. “It will add another sense of urgency to defeating” it, he said, “and that will be very hard to do without eliminating its sanctuary. If this doesn’t create in the world a fierce determination to rid ourselves of this scourge, I don’t know what will.”

Image Police officers outside the Bataclan music hall, which was a scene of carnage on Friday night. Credit... Pierre Terdjman for The New York Times

The Paris attacks will inevitably raise the question of whether to escalate American and Western military operations in Syria and Iraq. Mr. Obama has authorized airstrikes and sent small teams of Special Operations forces acting as advisers to aid Iraqi military units, Syrian rebels and Kurdish fighters on the ground. But he has strongly resisted a more extensive involvement of American ground troops to avoid repeating what he sees as the mistakes of the Iraq war.

In Mr. Obama’s view, the United States made things worse after Sept. 11 by invading Iraq and toppling Saddam Hussein, stoking a wider anti-American militant movement that ultimately led to the rise of the Islamic State. While critics fault him for pulling American troops out of Iraq in 2011, leaving a vacuum, he has long believed that a greater involvement by the United States would only entangle it in another quagmire without successfully resolving the conflict.

Ms. Townsend and others said that the White House had been too reluctant to acknowledge an “inconvenient truth” — that the Islamic State threat extends beyond the Middle East and could easily lead to a Paris-style attack in the United States.

If there were doubts about that before, American agencies on Saturday were busy trying to make sure that that was not the case, scouring passenger manifests on airliners bound for the United States and searching surveillance resources for chatter about plots.