WASHINGTON — Facing stiff political headwinds and a flagging election-year agenda, the most vulnerable Democrats in Congress have found a way to distance themselves from their leaders: demanding an end to stock trading for all members of Congress, including senior lawmakers who oppose the move.

The growing list of Democrats who have signed on to ethics legislation that would ban ownership of individual stocks is remarkably bipartisan, speaking to the political power of the issue. On the Democratic side, the names parallel the party’s list of endangered incumbents, many of whom rushed to sign on only after Speaker Nancy Pelosi of California had expressed her opposition.

“We introduced this in June 2020 and reintroduced it this Congress,” said Representative Abigail Spanberger of Virginia, a Democrat from a politically competitive district who wrote a stock ban with Representative Chip Roy of Texas, a conservative Republican. “We were steadily adding co-sponsors, but it is absolutely the case that the speaker’s answer to that question related to stock ownership and trading really ignited this as an issue.”

The legislation faces long odds on Capitol Hill, where Ms. Pelosi’s opposition — “We’re a free-market economy,” she has said — and the skepticism of other top Democrats make it unlikely to be considered. But the surge in interest underscores the political potency of the issue in Congress, an institution increasingly detested by the public, and the popularity of the specific idea of banning stock trading by lawmakers, which recent polls have shown is supported by a lopsided proportion of voters in both parties.

Last week, 27 House members signed on to a letter to Ms. Pelosi and Representative Kevin McCarthy of California, the top Republican, urging them “to swiftly bring legislation to prohibit members of Congress from owning or trading stocks.”

Signers included Democrats in some of the toughest districts in the country: Katie Porter of California, Jared Golden of Maine, Tom Malinowski of New Jersey, Angie Craig of Minnesota, Haley Stevens of Michigan and Matt Cartwright of Pennsylvania.

On the other side of the Capitol, Senator Jon Ossoff, Democrat of Georgia, piled on with his own bill, co-sponsored by Senator Mark Kelly of Arizona, one of the most endangered Democrats facing re-election this year. (Mr. Kelly sent out a fund-raising “petition” on the issue on Wednesday.)

Their bill — which would mandate that lawmakers put investments into a blind trust and ban the trading of individual stocks — has been joined by separate measures written by Senators Josh Hawley, Republican of Missouri, and Ben Sasse, Republican of Nebraska. Mr. Sasse’s version, drafted in 2018 and reintroduced on Wednesday, would go further, requiring presidents and vice presidents to release their tax returns and Congress to make public sexual harassment settlements, which have often been struck in secret.

The stock-trading push stems from a string of recent accusations that senators from both parties traded health care stocks after closed-door briefings on the coronavirus pandemic. The issue was front and center in the two Senate races in Georgia in 2020, and Mr. Ossoff hit his Republican opponent, the incumbent David Perdue, on it with brutal efficiency.

“I saw all this trading during the pandemic massively erode confidence in Congress,” Mr. Ossoff said. “Members of Congress have an unfair advantage when they’re making investment decisions. Whether or not it rises to the level of criminal insider trading, we know what legislation is likely to become law. We can draw inferences.”

The lawmakers caught up in the accusations still bristle. None were charged with insider trading, nor did they face repercussions from the House or Senate ethics committees.

Former Senator Kelly Loeffler of Georgia, who lost re-election to Raphael Warnock, defended her innocence on Sunday in the conservative Washington Examiner, blaming “a left-wing blog” and hypocritical Democrats who refuse to look at the investments of Ms. Pelosi’s affluent husband, Paul Pelosi, for what she called false accusations of insider trading. She suggested that the new bills banning stock trading were partisan efforts to deflect attention from Ms. Pelosi.

But at least one of the lawmakers, Senator Richard M. Burr of North Carolina, who was investigated by the Justice Department after he dumped hundreds of thousands of dollars of stock early in the pandemic, has said he welcomes the effort. “I’ll support whatever they come up with,” said Mr. Burr, who was never prosecuted and is retiring at the end of his term.

The bills enjoy broad support — the 42 co-sponsors of Ms. Spanberger’s TRUST in Congress Act include Representatives Matt Gaetz of Florida, Scott Perry of Pennsylvania and Andy Harris of Maryland, all firmly in the Trump wing of their party — and if anything, they are putting Ms. Pelosi in the spotlight.

“You have the speaker of the House out there trading, and her husband making millions and millions of dollars a year,” Mr. Hawley said.

Democrats are just as eager to contrast their position with Ms. Pelosi’s. Her flat refusal in December to consider a stock trading ban made the issue a cause célèbre. Two weeks ago, still under fire, she told reporters, “I just don’t buy into it, but if members want to do that, I’m OK with that.”

“The speaker, I don’t want to directly call her out, but handfuls of members have put dozens and dozens of years here. They come at this from a different time and a different perspective,” said Ms. Stevens, who has found herself almost certainly facing another Democrat, Andy Levin, in the upcoming House primaries in redistricted Michigan. Both signed on to last week’s letter demanding action on a trading ban.

Democratic leaders remain leery. They argue that once Congress begins trying to regulate its own members out of investments, it is difficult to draw the line between what is permissible and what is not. If stock ownership is forbidden because it could create a conflict with legislating, would having student loan debt make it inappropriate for a member to press for loan relief? Would owning real estate confer an improper personal interest in environmental or land-use policy?

Mr. Roy allowed that there were complexities, but, he said, a line has to be drawn.

“If you’re talking about dirt, well, are you talking about your family farm or are you engaging in thousands of real estate transactions?” he asked. “Are you buying and selling and engaging in commercial real estate transactions development while you’re in Congress? There are limits to what we’re supposed to do.”

Drew Hammill, Ms Pelosi’s deputy chief of staff, said that the speaker had asked Representative Zoe Lofgren, Democrat of California and the chairwoman of the Committee on House Administration, to examine noncompliance with the existing Stop Trading on Congressional Knowledge (STOCK) Act, and that she could support increasing the penalties under that 2012 law, which mandates disclosure of lawmaker trading.

Representative Steny H. Hoyer of Maryland, the House majority leader, said on Wednesday that he continued to believe lawmakers should be allowed to own and trade individual stocks, as long at they obey insider trading laws.

For Democrats pushing for the stock ban, such opposition is all for the best, at least politically. With such narrow margins in the House and the Senate, Democrats facing difficult re-election races do not have the latitude to try to show their independence by voting against major legislation, while hoping it passes — a common practice with larger majorities.

And clearly they believe voters are firmly on their side.

“In my experience, when I talk to people in Missouri they say, ‘Wait a minute, senators own and trade stocks?’” Mr. Hawley said. “It’s just a basic good-government issue, and it’s something that people understand.”