In the final hours before the midterm elections, some Americans say they are worried about federal interference in the vote and potential efforts by Republicans to overturn the results if the party is unsuccessful.

For years, President Donald Trump has sowed doubts about the nation’s electoral system by promoting debunked claims of mail-ballot fraud, faulty voting machines and voting rolls riddled with noncitizens. As polls show the Republican majority in Congress in peril, Trump has ramped up his baseless attacks, even dangling a $1 million reward to tipsters who help secure a voting-fraud conviction.

Some voters are nervous about what he might do next.

“I am very concerned that the election will be disrupted in ways that will affect the margins,” said Tiffany Hall, a 56-year-old physician who lives in a suburb of Cincinnati.

Civil rights groups and labor unions recently sued the Trump administration, seeking to block the potential deployment of federal agents at the polls.

Hall, who is Black, voted…