He was the first member of Congress caught up in the recent wave of allegations of sexual abuse and inappropriate behaviour.
Franken apologised yesterday, but the criticism only grew through the day. Fellow Democrats swiftly condemned his actions, mindful of the current climate as well as the prospect of political blowback.
Republicans, still forced to answer for the multiple allegations facing Alabama Senate candidate Roy Moore, joined in pressing for an investigation. Franken said he would welcome it.
Both had been performing for military personnel in Afghanistan two years before the one-time "Saturday Night Live" comedian was elected to the Senate.
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Tweeden said yesterday that before an earlier show Franken had persisted in rehearsing a kiss and "aggressively stuck his tongue in my mouth."
Franken, 66, was the latest public figure to be caught in the deluge of revelations of sexual harassment and misconduct that have crushed careers, ruined reputations and prompted criminal investigations in Hollywood, business and beyond.
The swift rebukes from both Republican and Democratic lawmakers suggest that momentum from the online #Metoo movement has begun to spur a culture shift on Capitol Hill, where current and former staffers say misogynistic and predatory behaviour has long been an open secret.
"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 realise were just plain offensive," Franken wrote.
"I respect women. I don't respect men who don't," he added. "And the fact that my own actions have given people a good reason to doubt that makes me feel ashamed."
Of the photo, Franken said: "I look at it now, and I feel disgusted with myself. It isn't funny. It's completely inappropriate. It's obvious how Leeann would feel violated by that picture."
Trump, who misspelled the name Frankenstein, referred to a New York magazine story from 1995 in which Franken, while a writer for "Saturday Night Live," suggested a skit in which "60 Minutes" commentator Andy Rooney would muse about drugging correspondent Leslie Stahl and taking pictures of her.
The accusations against Franken come just days after the Senate unanimously adopted mandatory sexual harassment training for members and staffs amid a flood of stories about harassment, sexual misconduct and gender hostility from staffers, aides and even female elected officials.
Senate Democrats spoke with one voice in describing Franken's actions as unacceptable and calling for an ethics probe.
Senator Claire McCaskill of Missouri, who is facing a tough re-election next year, said she was "shocked and concerned." She said, "Comedy is no excuse for inappropriate conduct, and I believe there should be an ethics investigation."
Senate Majority Leader Mitch McConnell, R-Ky., and the top Democrat, Chuck Schumer of New York, called for an ethics inquiry.