Millions have already cast ballots in the presidential race -- but for anyone feeling voter's remorse, a little-known election-law quirk allows for a do-over in some states.

At least four states allow voters to change or cancel their early-absentee ballots, including battlegrounds Michigan, Pennsylvania and Wisconsin.

The details vary from state to state.

In Wisconsin, absentee voters can change their ballots as many as three times before Election Day.

Wisconsin voters have gone for the Democratic nominee every presidential election year since 1988. This year, Republican presidential nominee Donald Trump trails Democratic nominee Hillary Clinton in the state by roughly 6 percentage points, according to the RealClearPolitics poll average.

But Wisconsin GOP Rep. Sean Duffy thinks voter concerns about Clinton -- including new revelations last week about her ongoing email controversy -- might encourage early-absentee voters to change their minds.

“Hard folks on the right and the left are not going to change their mind,” Duffy told “Fox & Friends” on Tuesday. “But you have these people in the middle who are ping-ponging as the information comes out. ... And as they have a gut check … no doubt that’s going to drive them to Donald Trump and put him over the top.”

Wisconsin voters can either request a new, mail-in ballot before 5 p.m. on Nov. 3 or complete a new in-person absentee ballot before 5 p.m. on Nov. 5.

Roughly 22 million Americans have already cast a vote -- through a combination of absentee ballots, voting by mail or at the polls.

The 2016 White House race, with seven days remaining, continues to be a close contest between Trump and Clinton, with Libertarian Party candidate Gary Johnson and Green Party candidate Jill Stein significantly trailing the two major-party candidates.

Pennsylvania also allows absentee voters to change their mind by voting in person on Nov. 8 Election Day.

“The really important one is Pennsylvania because that is one of the states that Donald Trump says is a must-win for him,” political analyst Erin McPike told Fox News on Tuesday. “That is the real state to watch.”

In Michigan, absentee voters can change their ballots by getting a new one from their local clerk’s office by 4 p.m. on Nov. 7.

The fourth state, Minnesota, has voted for the Democratic nominee every presidential election since 1976.

The state allows absentee voters to change ballots three ways, but the deadline is Tuesday.

They can, after cancelling their ballot, request a new mail-in ballot, vote in person before 5 p.m. on Nov. 7 or vote on Election Day.