The Republican Party and its conservative allies are engaged in an unprecedented legal campaign targeting the American voting system. Their wide-ranging and methodical effort is laying the groundwork to contest an election that they argue, falsely, is already being rigged against former President Donald J. Trump.

The campaign involves a powerful network of Republican lawyers and activist groups, working loosely in concert with the Republican National Committee. Many of the key players were active in Mr. Trump’s attempt to overturn the results of the 2020 election.

But unlike the chaotic and improvised challenge four years ago, the new drive includes a systematic search for any vulnerability in the nation’s patchwork election system.

Mr. Trump’s allies have followed a two-pronged approach: restricting voting for partisan advantage ahead of Election Day and short-circuiting the process of ratifying the winner afterward, if Mr. Trump loses. The latter strategy involves an ambitious — and legally dubious — attempt to reimagine decades of settled law dictating how results are officially certified in the weeks before the transfer of power.

At the heart of the strategy is a drive to convince voters that the election is about to be stolen, even without evidence. Democrats use mail voting, drop boxes and voter registration drives to swing elections, they have argued. And Mr. Trump’s indictments and criminal conviction are a Biden administration gambit to interfere with the election, they claim.

“As things stand right now, there’s zero chance of a free and fair election,” Mike Howell, a project director at the Heritage Foundation, a conservative think tank, said at an event this week. “I’m formally accusing the Biden administration of creating the conditions that most reasonable policymakers and officials cannot in good conscience certify an election.”