WASHINGTON (AP) — Election Day is hitting with an additional layer of tension after weeks of uncertainty about the security of voting systems and threats of intimidation at the polls.

Unsupported claims by Republican presidential candidate Donald Trump of a rigged election, fears that hackers might attack election systems, and concerns about voter intimidation or fraud have clouded the run-up to Tuesday's vote.

One positive sign is the lack of any significant trouble during early voting, which could account for as much as 40 percent of the overall vote.

Presidential elections usually include sporadic voting problems, such as machines not working properly, long lines and issues with ballots or voter rolls. The question is whether problems this year will be widespread and indicate a pattern of fraud or intimidation.