NEW YORK — For much of the year, Kirsten Gillibrand’s critics — sensing a presidential aspirant in their midst — had assumed that the New York senator could not hear enough about herself. For one day at least, it appeared she had.

It had been about 10 hours since President Trump accused her of “begging’’ for campaign contributions that she “would do anything’’ to secure, and Gillibrand, driving with her 14-year-old son on Tuesday evening, flipped on the radio looking for an update on the Senate race in Alabama. The top story, instead, was her. The radio went off again.

What, exactly, had the president said about her? her son asked.

“He thinks mommy is doing a bad job,’’ she recalled telling him.

After a Senate career spent elevating victims of sexual harassment and assault as a defining political focus, Gillibrand has assumed her place at the head table of the Democrats’ anti-Trump movement.

Her cause became the country’s, and she has made sure to stay out front.

Gillibrand was the first in her caucus to say that Senator Al Franken, a Minnesota Democrat, should resign. She was the first prominent Democrat to say President Bill Clinton should have left office for his own sexual misconduct in the 1990s.

She called for Trump to step down, citing what she called his numerous and credible accusers. Then came Trump’s Twitter counterpunch, which was viewed by some as innuendo-laden and which Gillibrand denounced as a “sexist smear.’’

Yet Gillibrand’s strengthening hand in national Democratic politics owes to more than mere circumstance. Circumstance does not transform an upstate congresswoman, who once boasted of keeping guns under her bed and pushed English as the official language of the United States, into an avatar of liberalism in 2017.

Ever since her longshot entrance into a 2006 House race against an entrenched Republican in a conservative district, Gillibrand has been underestimated.

Colleagues in the House once derided her as “Tracy Flick,’’ the hyper-ambitious blonde played by Reese Witherspoon in the movie “Election.’’ And when David A. Paterson, New York’s governor at the time, made her the shock pick to fill Hillary Clinton’s Senate seat in 2009, she was immediately seen as vulnerable, especially from the left.

“She had very middle-of-the-road points of view,’’ Paterson said. “It just kind of appeared that she sort of flipped. I think in retrospect, it would have been better to evolve.’’

That knock has not stuck, and she appears to be looking at the next rung of the political ladder. While Gillibrand and her political team play down all talk of 2020, saying she is focused on her own 2018 reelection and those of her fellow Senate Democrats, she has for months been doing the type of spadework endemic to past presidential candidates: expanding her fund-raising network, courting key constituencies, such as black voters, and polishing her image nationally.

She sat for a recent Vogue feature, complete with a photo spread by Annie Leibovitz, that included this cover teaser: “2020 Vision: All Eyes On Kirsten Gillibrand.’’

She has blitzed the liberal news media, including podcasts of former Obama administration officials, “Pod Save America’’ and “Lovett or Leave It.’’ She has cursed freely in public, a recurring tic in her career — registering more recently as a brashness to match Trump.

Long a talented fund-raiser, Gillibrand has cultivated a flourishing network of small donors, raising nearly $3 million in the first three quarters of 2017 from people who gave less than $200, more than she had in the previous eight years combined from such donors.

Her moment at center stage follows notable turns from some other members of the “2020 caucus,’’ as some on Capitol Hill have labeled the presidentially curious.

Senator Elizabeth Warren, a Massachusetts Democrat, found her catchphrase in February, courtesy of Republican Senator Mitch McConnell of Kentucky, the majority leader, who led a push to formally silence her for impugning a colleague on the Senate floor.

“Nevertheless, she persisted,’’ he complained, and Warren has repeated the comment with pride.