In the wake of the riot on Capitol Hill on Jan. 6, 2021, a groundswell built in Washington to rein in the onslaught of lies that had fueled the assault on the peaceful transfer of power.

Social media companies suspended Donald J. Trump, then the president, and many of his allies from the platforms they had used to spread misinformation about his defeat and whip up the attempt to overturn it. The Biden administration, Democrats in Congress and even some Republicans sought to do more to hold the companies accountable. Academic researchers wrestled with how to strengthen efforts to monitor false posts.

Mr. Trump and his allies embarked instead on a counteroffensive, a coordinated effort to block what they viewed as a dangerous effort to censor conservatives.

They have unquestionably prevailed.

Waged in the courts, in Congress and in the seething precincts of the internet, that effort has eviscerated attempts to shield elections from disinformation in the social media era. It tapped into — and then, critics say, twisted — the fierce debate over free speech and the government’s role in policing content.

Projects that were once bipartisan, including one started by the Trump administration, have been recast as deep-state conspiracies to rig elections. Facing legal and political blowback, the Biden administration has largely abandoned moves that might be construed as stifling political speech.

While little noticed by most Americans, the effort has helped cut a path for Mr. Trump’s attempt to recapture the presidency. Disinformation about elections is once again coursing through news feeds, aiding Mr. Trump as he fuels his comeback with falsehoods about the 2020 election.