Ms. Dunham’s prominence in the Clinton campaign made her comments particularly resonant. Mrs. Clinton leaned on Ms. Dunham’s support so heavily that the actress and writer was awarded a prime speaking slot at the Democratic National Convention in Philadelphia. (“Hi, I’m Lena Dunham and according to Donald Trump, my body is probably, like, a 2.”)
Ms. Dunham’s statement to The Times that she had warned the Clinton campaign about Mr. Weinstein came not long after she had stirred controversy by publicly defending a “Girls” writer, Murray Miller, who had been accused of sexual assault. A torrent of criticism followed Ms. Dunham’s words of support for Mr. Miller, whose lawyers “categorically and vehemently” denied the allegation. Three days after her defense of her colleague, Ms. Dunham posted an apology on Twitter. “Under patriarchy, ‘I believe you’ is essential,” it read, in part.
Her defense of the accused writer was not the first time Ms. Dunham had gone against the prevailing views of those in her circle. After a 2015 dinner party at the Park Avenue apartment of Richard Plepler, the chief executive of HBO, several guests said that Ms. Dunham had expressed discomfort with how the Clintons and their allies had discredited the women who said they had had sexual encounters with or had been sexually assaulted by former President Bill Clinton — an issue that many Democrats have reassessed in recent weeks.
The Times reported on Ms. Dunham’s dinner party remarks last January. At the time, her spokeswoman, Cindi Berger, said the description of her comments was a “total mischaracterization.”
By then, the alliance between the candidate and the star had become critical, with Ms. Dunham touring the country to help boost enthusiasm in a Democratic primary season that saw many young women gravitate to Senator Bernie Sanders of Vermont.
Mrs. Clinton had started her campaign by promising that her victory would lead to “an America where a father can tell his daughter: ‘Yes, you can be anything you want to be. Even President of the United States.’” But as Mr. Sanders’s anti-Wall Street message took hold, the Clinton campaign realized millennial women were a stubborn demographic, less inclined to feel the same gender allegiance as their mothers.
A Harvard Institute of Politics survey released at the time found that 38 percent of women aged 18 to 29 said they were supporting Mrs. Clinton in the primary, compared with 40 percent for Mr. Sanders. (In the general election, Mrs. Clinton would go on to overwhelmingly win young women — 63 percent to Mr. Trump’s 31 percent, according to exit polls.)
In Ms. Dunham, the campaign had found a bona fide celebrity feminist spokeswoman who Mrs. Clinton’s aides believed could connect to the younger women were Feeling the Bern. The “Girls” creator made stops in New Hampshire and Iowa, where she spoke to young women often wearing custom-made dresses emblazoned with “Hillary.”
“My underwear say ‘feminist’ on the butt!” she told a crowd in Iowa City.
Even in a campaign with no shortage of famous surrogates, Ms. Dunham stood out. She took over the candidate’s Instagram account and conducted an extensive interview with Mrs. Clinton for Lenny Letter, the feminist online newsletter founded by Ms. Dunham and the “Girls” showrunner Jennifer Konner.
Ms. Dunham also hosted fund-raisers, including one at Soho House in Manhattan. She was also among the boldface names, including Billy Crystal, Bernadette Peters and Julia Roberts, who attended a Broadway gala that Mr. Weinstein helped produce.
For years, Mr. Weinstein had been a loyal friend and donor to Bill and Hillary Clinton. In 2014, the Clintons rented a seven-bedroom bluff-side estate in Amagansett, N.Y., next door to Mr. Weinstein’s Hamptons home. After the November election, the Clintons dined with Mr. Weinstein and discussed a possible documentary project. The talks fell apart soon after the first allegations against him were published in The Times on Oct. 5.
On Oct. 10, as the accusations against Mr. Weinstein mounted with the publication of a second Times article and another in The New Yorker, by Ronan Farrow, Mrs. Clinton said she was “shocked and appalled by the revelations” and that “the behavior described by women coming forward cannot be tolerated.”
The inevitable second-guessing that follows any election loss has set in like a chronic condition in Mrs. Clinton’s world. While Ms. Dunham says she has questioned the campaign’s close association with Mr. Weinstein, other Clinton allies have lately pointed to the reliance on liberal celebrities, and Ms. Dunham in particular, as evidence that the campaign had been out of touch with voters during an off-with-their-heads election year.
These allies have wondered whether, despite Ms. Dunham’s hard work for Mrs. Clinton and the sprinkling of some millennial stardust on the campaign trail, the New York-born star potentially turned off voters whom Mrs. Clinton needed to reach.
Ahead of the caucuses, Simone Frierson, a recent graduate of the University of Iowa, told The Times that the season of Ms. Dunham’s HBO series partly set in Iowa “made fun of Iowans a little.” Ms. Frierson added that the “Girls” episodes in which Ms. Dunham’s character, Hannah Horvath, briefly studies at the esteemed Iowa Writers’ Workshop “made us seem like we’re simple.”
In the final days of the campaign, Ms. Dunham made a video short for the comedy website “Funny or Die” that played on the criticism she had faced as a prominent Clinton supporter. In it, she makes a diverse set of friends cringe as she performs a pro-Hillary rap as “MC Pantsuit.”
“I wonder if I’m actually hurting her chances of winning?” a bikini-clad Ms. Dunham says at the end.
After Mrs. Clinton’s unexpected defeat, Ms. Dunham was more serious about blame that had been cast her way, telling Rolling Stone, “It’s amazing. I’m like, ‘Why don’t we check in with Russia, you guys?’”