In the weeks leading up to Election Day, election deniers voiced their concerns online about possible widespread voter fraud that might compromise the results — a phenomenon that, according to officials, has not been observed in modern elections. On Tuesday, even before polls closed, former President Donald J. Trump alleged “massive CHEATING” in Philadelphia.

When the results came in, showing strong support for Mr. Trump, the once-loud voices calling out for election integrity fell noticeably silent.

“When it looked like Trump was going to win, the election denialism became very, very quiet,” commented Welton Chang, co-founder and CEO of Pyrra Technologies, a firm that monitors fringe social networks.

This sudden quiet among election deniers after Mr. Trump’s success on Tuesday highlights the strategic nature of the narrative, aimed primarily at empowering Mr. Trump and contesting election outcomes, experts explain. Once the denial narrative no longer served a political purpose, influencers and Trump allies appeared willing to let it drop.

The unfounded belief that the 2020 election was stolen extended beyond social media, fueling a large-scale movement of “election integrity” activists. Over the past four years, many had become poll watchers, election workers, and even election board members, aiming to “secure” the voting system against a repeat “steal.”

During Tuesday’s vote, some prominent members of the movement posted claims online, implying activists were uncovering issues.

By Wednesday, a top leader credited Mr. Trump’s victory to their efforts to safeguard the system.

“To the thousands of election integrity warriors: Thank you,” wrote Cleta Mitchell, a leading figure in the movement, on X on Wednesday.

In an interview, Ms. Mitchell claimed that the activists’ vigilance had prevented the kind of issues seen in 2020. When asked about those who might view this acceptance of results as politically motivated, she advised them to “get over their Trump derangement syndrome.”

False claims about extensive fraud in Pennsylvania and other swing states surged on X early on Election Day but waned as the night continued, reported the Center for an Informed Public at the University of Washington.

On Telegram, dozens of far-right channels previously identified by The New York Times spent days questioning the vote’s integrity, with some suggesting a need for force to block perceived fraud. As results came in, their tone shifted from wary to triumphant.

“Most of our Proud Boy poll workers have returned home,” read a post at 6:35 p.m. from a North Carolina chapter of the extremist group involved in the January 6 Capitol riot. “They said that despite media claims, they believe Trump will take North Carolina.”

Another instance of the movement’s abrupt shift in tone occurred in Milwaukee. Social media feeds filled with suspicion after election administrators there found that 13 ballot tabulators had been inadequately secured. Officials announced a need to recount 31,000 votes.

Ms. Mitchell cited the Milwaukee incident as evidence of her movement’s improvements. “Instead of putting cardboard on the windows,” she wrote on X, the Milwaukee election director pledged to “recount all those ballots for accuracy.”

Seth Keshel, an Arizona election denier who has traveled the country spreading voter fraud claims, took a nuanced stance: he believed Mr. Trump won fairly but suggested that there might have been fraud in down-ballot races where Democrats led.

“I believe the outcome is correct,” Mr. Keshel stated. “But I don’t think every state is accurate.”

On X, a channel connected to Elon Musk’s political action committee circulated similar claims, suggesting fraud in congressional races led by Democrats. Some posts inaccurately pointed to vote spikes as evidence, though this is a common occurrence in elections and not indicative of wrongdoing.

By Wednesday morning, the strongest voices questioning the presidential race outcome on X were from the left, according to NewsGuard, a misinformation-monitoring firm — though these claims didn’t reach the scale of the Trump-backed “Stop the Steal” movements of 2020.

The hashtag #DoNotConcedeKamala had over 386,406 mentions by 3 p.m. on Wednesday, as tracked by NewsGuard. Many posts echoed earlier far-right allegations, including unproven theories about foreign interference or mass ballot destruction.

“The spread is undeniable, but it hasn’t hit mainstream,” said Steven Brill, NewsGuard’s co-founder. “Most prominent left-wing claims about election rigging are from lesser-known X users.”

By noon, posts alleging “missing votes” for Ms. Harris peaked at more than 94,000 per hour, according to data from analytics firm PeakMetrics. votes” for Ms. Harris had peaked at more than 94,000 per hour, according to an analysis by PeakMetrics, an analytics company.