Earlier, response from Republicans and Democrats alike was swift and unsparing. Mitch McConnell, Republican of Kentucky and Chuck Schumer, Democrat of New York, the Senate leaders, wasted no time before forwarding the matter to the Senate Ethics Committee — a move supported by Democrats, including Mr. Franken. Lawmakers did stop short of meting out a punishment on a fellow senator, and it appeared that Mr. Franken would be able to weather the disclosure.

“As with all credible allegations of sexual harassment or assault, I believe the Ethics Committee should review the matter,” Mr. McConnell said in a statement. “Regardless of party, harassment and assault are completely unacceptable — in the workplace or anywhere else.”

Democrats gave Mr. Franken no quarter.

“This is unacceptable behavior and extremely disappointing. I am glad Al came out and apologized, but that doesn’t reverse what he’s done or end the matter. I support an ethics committee investigation into these accusations and I hope this latest example of the deep problems on this front spurs continued action to address it,” said Patty Murray of Washington, one of the most senior Democratic women in the Senate.

The realm of comedy, which spawned the charges against Louis C.K., has been particularly suspect, and Mr. Franken, who emerged from “Saturday Night Live” as a nationally known celebrity, appeared to acknowledge that.

“Coming from the world of comedy, I’ve told and written a lot of jokes that I once thought were funny but later came to realize were just plain offensive,” he wrote. “But the intentions behind my actions aren’t the point at all. It’s the impact these jokes had on others that matters. And I’m sorry it’s taken me so long to come to terms with that.”