– Democratic Party leaders united Wednesday in calling for Sen. Al Franken to resign from the U.S. Senate, an extraordinary rebuke to the Minnesota Democrat as he faced a new allegation of sexual harassment.

Franken planned to make an announcement about his future Thursday morning on the Senate floor.

His office said it would happen at 10:45 a.m. Central time, describing it as the senator planning to "deliver a speech from the Senate floor."

A top Democratic official told the Star Tribune that Franken planned to resign, but the senator’s staff insisted no final decision had been made.

It was clear that Franken’s political career was hanging by a thread, as a wave of Democrats throughout the day — first female senators, followed by many male colleagues and then other party leaders, said it was time for him to step down from the seat he’s held since 2009.

“I believe it would be better for our country if he sent a clear message that any kind of mistreatment of women in our society isn’t acceptable by stepping aside to let someone else serve,” New York Sen. Kirsten Gillibrand, the first of Franken’s Democratic colleagues to come out against him, posted on Facebook.

Politico reported that a former Democratic aide says Sen. Al Franken tried to forcibly kiss her in 2006.

If Franken resigns, DFL Gov. Mark Dayton will appoint a temporary replacement. A high-ranking Democratic source told the Star Tribune that the likeliest replacement is Lt. Gov. Tina Smith, a close Dayton ally who would not be expected to run for the seat in an ensuing special election in November 2018. Dayton is expected to move quickly if Franken resigns.

Franken’s day started when another woman stepped forward with allegations of unwanted touching. More than half a dozen women have shared stories of being groped, harassed or forcibly kissed by the Minnesota ­Democrat and former “Saturday Night Live” performer, both before and after his Senate election. Franken has repeatedly apologized, while saying the issue should be turned over to a Senate Ethics Committee investigation.

But the bruising round of denunciations, including from his closest colleagues and ideological allies, arriving in bursts throughout the afternoon, made that an increasingly untenable prospect.

More than half of Franken’s fellow Democrats in the U.S. Senate said he should step down, including Senate Minority Leader Chuck Schumer of New York. Democratic National Committee Chairman Tom Perez also joined in.

“I consider Senator Franken a dear friend and greatly respect his accomplishments, but he has a higher obligation to his constituents and the Senate, and he should step down immediately,” said Schumer, one of Washington’s most powerful Democrats.

The decision by Democrats to abandon Franken comes as President Donald Trump and other prominent Republicans have embraced the Senate candidacy of Alabama’s Roy Moore, despite allegations by multiple women that Moore sexually abused them, including some who were teenagers at the time. The move against Franken, paired with the forced retirement of longtime Democratic Rep. John Conyers over sexual harassment, seem intended by Democratic leaders to draw a bright line between the two parties on their response to such accusations.

The shunning of Franken is perhaps the most dramatic case of a party turning on one of its own since Sen. Mitch McConnell led the Republican effort to force Robert Packwood of Oregon from the Senate in 1995, after Packwood was found to have engaged in sexual harassment and misconduct. And it represents the harshest treatment handed out to a U.S. senator from Minnesota since a 96-0 vote in 1990 to denounce then-Sen. Dave Durenberger, a Republican, for bringing ‘’dishonor and disrepute’’ to the institution through improper financial dealings.

Prominent Minnesota DFLers, who with few exceptions had refrained from demanding Franken’s resignation in recent weeks, also changed their views Wednesday. They included U.S. Reps. Betty McCollum, Keith Ellison and Tim Walz, who all agreed that Franken must step down.

Minnesota’s senior U.S. senator, Amy Klobuchar, stopped short of directly calling for resignation, but said in a statement: “Sexual harassment is unacceptable. This morning I spoke with Senator Franken and … I am confident he will make the right decision.”

Just a day earlier, Franken seemed positioned to try to ride out the storm. He made the media rounds, promising to win back the trust of Minnesota voters, then resumed his normal duties, sitting in on hearings, railing against the Senate tax bill and the FCC’s upcoming decision on net neutrality.

Dozens of women who have worked with Franken, both in the Senate and from his time on “Saturday Night Live,” stepped forward to testify that he had always treated them with respect.

His office’s upbeat tone shifted abruptly after Politico published an account from a woman, identified only as a former Democratic congressional aide, who said Franken tried to forcibly kiss her after a taping of his radio show in 2006. She told the newspaper that she ducked to avoid his lips, and as she hurried out of the room, he called after her: “It’s my right as an entertainer.”

Franken’s office flatly denied the story.

“This allegation is categorically not true and the idea that I would claim this as my right as an entertainer is preposterous,” Franken said in a statement.

But as calls for his resignation came raining down, the tone shifted. “Senator Franken will be making an announcement tomorrow. More details to come,” his office said in a terse tweet that drew thousands of responses — a mix of vitriol, support and mentions of different standards for Moore and Trump, who was elected despite allegations of sexual harassment from more than a dozen women.

Comparisons to Trump and Moore were particularly galling for Franken, who had spent his Senate career building a reputation as a forceful advocate for women. He had been an enthusiastic supporter for women who stepped forward to share stories of harassment and assault by powerful men, and even after he himself was accused, took pains to say “we need to listen to and believe women’s experiences.”

From left, Sen. Kirsten Gillibrand, D-N.Y., accompanied by Rep. Cheri Bustos, D-Ill., and former Fox News host Gretchen Carlson, speaks at a news conference where she and other members of congress introduce legislation to curb sexual harassment in the workplace, on Capitol Hill, Wednesday, Dec. 6, 2017, in Washington. Gillibrand and fellow female Democratic senators have united in calling for Sen. Al Franken to resign amid sexual misconduct allegations.

After eight years in the Senate, Franken had emerged as a powerful voice on progressive causes and forceful critic of the Trump administration, frequently generating national headlines with aggressive questioning of the president’s Cabinet officers. He was a star for the Democratic Party, raising millions of dollars for its candidates across the country and appearing frequently on nationally broadcast talk shows and in other high-profile venues.

That image came crashing down Nov. 16, when a fellow performer said he forcibly kissed her during a 2006 USO show, and shared a photo of Franken mugging for the camera with his hands hovering over her breasts as she slept on the plane home.

Candidates started giving his donations away to charities that serve battered women. A Minnesota rape victim asked Franken to take his name off a bill he had sponsored in her honor.

Some of the allegations date back to Franken’s celebrity career, before his Senate run. He was hired as a staff writer for “Saturday Night Live” in its first season in 1975, and quickly became a regular on-air performer as well. He served two long stints on the show, the second ending in 1995. After that, he published several bestselling books of political satire from a liberal point of view, and hosted a nationally syndicated radio show for several years.

In their denunciations of Franken, Democratic Party leaders seemed to be trying to convey a message that the party has a zero-tolerance approach to instances of sexual harassment by its own officials.

“The Democratic Party will stand up for women and what is right,” said Perez, the national Democratic chairman. “Public service is a public trust. If you are a candidate for office or an elected official who has engaged in sexual misconduct, you should step aside — whether you sit in the U.S. House of Representatives, the U.S. Senate or the Oval Office.”