“Politically, I get the ‘let’s trip up the other side, make them fail’ strategy,” he said. “But what’s more important, to win extra seats or to shape the most important piece of social legislation since the 1960s? It was a go-for-all-the-marbles approach. Unless they produced an absolute failure for Mr. Obama, there wasn’t going to be any political benefit.”

Image House members who opposed the bill acknowledged protesters on Sunday. Republicans said the bill had energized their voters. Credit... Stephen Crowley/The New York Times

Republicans also face the question of what happens if the health care bill does not create the cataclysm that they warned of during the many months of debate. Closing out the floor debate on Sunday night, the House Republican leader, Representative John A. Boehner of Ohio, warned that the legislation would be “the last straw for the American people.” Representative Marsha Blackburn, Republican of Tennessee, proclaimed several hours earlier, “Freedom dies a little bit today.”

Yet there are elements of the bill, particularly in regulating insurers, that could well prove broadly popular, and it could be years before anyone knows whether the legislation will have big effects on health care quality and the nation’s fiscal condition. Indeed, most Americans with insurance are unlikely to see any immediate change in their coverage, and several Republicans warned that the party could pay a price for that.

“When our core group discover that this thing is not as catastrophic as advertised, they are going to be less energized than they are right now,” Mr. Frum said.

He warned that the energy Republicans were finding now among base voters would fade.

The head of the Democratic Senatorial Campaign Committee, Senator Robert Menendez of New Jersey, offered a similar argument. “When this bill goes into effect, and none of the things Republicans warned about begin to happen — none of the death panels, none of the government takeover, none of the socialism — Republicans will have no credibility,” Mr. Menendez said.

The final deliberations, which drew protesters from across the country, including many Tea Party activists, cast an angry tone to the proceedings that also stirred concern among some Republicans. Some Democratic lawmakers said they had been taunted with racial epithets and homophobic slurs as they walked into the Capitol over the weekend to vote. Representative Randy Neugebauer, Republican of Texas, shouted out “baby-killer” on the House floor when Representative Bart Stupak of Michigan, one of the most fervent Democratic opponents of abortion in the House, outlined a deal he had worked out with the White House, which he said assured that the health care bill would not finance abortions.