WASHINGTON – The Senate Ethics Committee formally launched an investigation into Sen. Al Franken on Thursday, hours after another woman said the Minnesota senator groped her.

As allegations mounted against Franken, several fellow Democratic members of Congress said Thursday that he should resign. Rep. Joe Crowley of New York, the chairman of the House Democratic Caucus, and Rep. Tim Ryan of Ohio said separately that it's time for Franken to go.

"These are credible allegations, and I believe these women," Ryan tweeted, in reference to allegations against both Franken and U.S. Rep. John Conyers of Michigan, also a Democrat. Franken so far has resisted calls to resign, instead supporting the Ethics Committee investigation.

"While the Committee does not generally comment on pending matters or matters that may come before it, in this instance, the Committee is publicly confirming that it has opened a preliminary inquiry into Senator Franken's alleged misconduct," read a letter from the six-member Ethics Committee, comprised of three Republicans and three Democrats.

In the latest allegations, an Army veteran accused Franken of groping her. Stephanie Kemplin told CNN that Franken threw an arm around her and cupped her breast as she posed with him after a USO show while she was deployed in Kuwait in December 2003.

For the past two weeks, Franken has been battered by a series of accounts from women, both named and unnamed, who say they were groped, harassed or made to feel uncomfortable by the senator.

Franken's office responded to Kemplin's account with a variation of the response it has given to other allegations from women in recent days: "As Sen. Franken made clear this week, he takes thousands of photos and has met tens of thousands of people and he has never intentionally engaged in this kind of conduct. He remains fully committed to cooperating with the ethics investigation."

The latest CNN story broke on a day when Capitol Hill was already reeling from other sexual harassment scandals. Texas Republican Rep. Joe Barton announced Thursday he would not seek re-election next year. A nude photo of Barton surfaced online last week and the congressman admitted to extramarital affairs.

Conyers, a Michigan Democrat who is the longest-serving member of Congress, is under mounting pressure to resign after a string of harassment allegations. After one of his accusers appeared on TV to detail the $27,000 sexual harassment settlement she received from Conyers' office, House Democratic leader Nancy Pelosi and House Speaker Paul Ryan both called on the 88-year-old Conyers to step down.

Conyers' attorney pointed to Franken's continued Senate service as a reason for the congressman to stay in the seat he has held for almost 53 years. "At the end of the day, Nancy Pelosi is going to have to explain, what is the discernible difference between Al Franken and John Conyers?" attorney Arnold Reed told the Detroit News Thursday.

Franken, meanwhile, kept to his public schedule Thursday, participating in a Senate Health Committee hearing on the opioid crisis and preparing for a long evening of floor votes. But the new allegations shadowed him as he tried to get back to business as usual.

"I think it's time for Sen. Franken to go," Crowley told Politico Thursday. Several other House Democrats have echoed the call for Franken's resignation.

The conservative Daily Caller posted footage of one of its reporters trailing Franken up a stairwell asking him repeatedly if he was part of a "war on women."

Back home, a handful of DFL candidates, including gubernatorial hopefuls Erin Murphy and Rebecca Otto, said after the first allegations against Franken that he should resign. On Thursday, Joe Sullivan, one of several DFLers running for southern Minnesota's open First District congressional seat, also called for Franken's resignation, saying elected officials "should be held to a higher standard."

Video (02:54) VIDEO: Sen. Al Franken spoke to the media on Capitol Hill Monday in response to accusations that he groped two women.

Franken was also finding support, at times from unusual political quarters. Commentator John Ziegler wrote a column in USA Today that Franken's backers shared widely with the media Thursday. Ziegler, a conservative talk show host and media critic, argued that the press rushed to judgment by relaying Los Angeles radio host Leeann Tweeden's account of being groped and forcibly kissed by Franken on a 2006 USO tour without questioning details in Tweeden's recollection of events.

But Jennifer DeJournett, a Minnesota GOP activist who leads Voices of Conservative Women, said she's gotten almost 16,000 signatures on a petition for Franken to resign. She said that should count for at least as much as several groups of women who have publicly signed letters in support of Franken.

"I don't know how many women it's going to take before the women who signed on to support Sen. Franken will realize that they've made a mistake," DeJournett said.

Rep. Jennifer Schultz, DFL-Duluth, who attended a recent rally against sexual harassment at the State Capitol, said she believes Franken must make his own decision about whether to resign. She said any punishment should fit the severity of the harassment. But she wants Franken to speak more publicly about the allegations.

"He probably needs to be much more forward and transparent and answer any question that comes to him," Schultz said.

Kemplin, meanwhile, said she was a longtime fan of "Saturday Night Live" when she got in line for a photo with Franken at the 2003 USO appearance.

"When he put his arm around me, he groped my right breast," CNN quoted her as saying. "He kept his hand all the way over on my breast. I've never had a man put their arm around me and then cup my breast. So he was holding my breast on the side."

A photo provided by Kemplin, who was 27 at the time, shows her smiling, with her body angled toward Franken, his hand on her back. She told CNN she turned her body to shift Franken's hand off her breast. "I remember clenching up and how you just feel yourself flushed," she continued. "And I remember thinking — is he going to move his hand? Was it an accident? Was he going to move his hand? He never moved his hand. … It was long enough that he should have known if it was an accident. I'm very confident saying that."

Star Tribune staff writer Paul Walsh contributed to this report.