WASHINGTON — Donald Trump’s campaign and the Republican National Committee have paid at least $1.8 million to a political operative whose roster of companies include several that have been repeatedly investigated for voter registration fraud, even as Trump has complained that the election is rigged against him.

Three employees of Strategic Allied Consulting, a firm owned by conservative operative Nathan Sproul, pleaded guilty in Florida four years ago to felony charges related to altering and destroying scores of voter registration forms. There were no formal actions against the firm.

Yet recent federal campaign finance reports show Sproul is now back on the RNC’s payroll, this time with a firm named Lincoln Strategy Group. That’s a renamed version of his former firm Sproul & Associates, an Arizona-based company that was investigated for alleged voter registration misconduct in Nevada and Oregon.

Although Sproul was never charged in the 2012 Florida case, GOP officials and Mitt Romney’s presidential campaign considered the charges against his employees alone serious enough to fire his company in 2012. The chairman of the RNC said this week he didn’t know Sproul’s firm has been rehired. Neither the Republican Party nor the Trump campaign would discuss the specifics of the work Sproul or the firm is doing and in what states.

“We have zero tolerance for any threat to the integrity of elections,” Sean Spicer, RNC spokesman, said in September 2012. “When we were informed of an alleged incident, we immediately cut all ties to the company.”

The RNC paid Sproul’s company a total of $1.2 million in October for get-out-the-vote efforts. Records show Donald J. Trump For President Inc. paid another $600,000 to Lincoln Strategy on Oct. 27.

RNC Chairman Reince Priebus said he didn’t know his organization was still doing business with Sproul.

RNC spokeswoman Lindsay Walters declined to provide specific details about Sproul’s current work for the party. In past years, the RNC’s full spending with Sproul’s firms wasn’t disclosed in campaign finance reports until after the election.