A U.S. House special election in North Carolina’s 9th congressional district on Tuesday is essentially a do-over after a candidate’s 2018 victory was negated by allegations of illegal ballot harvesting. The election could flip a longtime Republican district, and has shifted national attention to the issue of ballot harvesting, the arguments in favor of and against it, and how different states regulate the practice.

Republican Mark Harris appeared to beat Democrat Dan McReady by 905 votes in the initial election last year, winning a seat in the House of Representatives. But fraud allegations against members of Harris’ campaign team nullified the results. One of Harris’ paid campaign workers, who had previously worked for Republican and Democratic candidates, was indicted by a grand jury for illegal ballot harvesting and ballot handling along with four of his assistants. Testimony included charges of forging signatures, filling out ballots to favor their candidate, and enabling an ineligible person to vote. Meanwhile, Harris isn’t running a second time; state Sen. Dan Bishop is now running against McReady for the seat. The race could prove decisive in determining the House majority ahead of the 2020 election, and is important enough to prompt President Donald Trump to hold a rally in Fayetteville on Monday night.