The final day of voting in this year's midterm elections arrives Tuesday against a backdrop of uncertainty after a year in which President Donald Trump has tried to interfere in how states run their elections and sown doubts about the outcome should Republicans lose.

Millions of Americans already have cast their ballots, with early voting turnout on pace to eclipse that of the last midterm elections.

In contrast to the president's continued rhetoric about election cheating, voting so far has unfolded with relatively few problems.