Eau Claire, Wisconsin (CNN) Donald Trump set his sights on an unlikely demographic as he pitched himself to voters Tuesday night in Wisconsin: those who have already cast their ballots for his rival Hillary Clinton.

The Republican nominee issued what he dubbed a "public service announcement" and urged early voters "having a bad case of buyer's remorse" to switch their votes and support him. And in Wisconsin and a handful of other states, they actually can, legally.

"A lot of things have happened over the last few days," Trump said, after hammering Clinton over her use of a private email server in light of the FBI's review of newly discovered emails that may be tied to that investigation.

"This is a message for any Democratic voters who have already cast their ballots for Hillary Clinton and are having a bad case of buyers' remorse -- in other words you want to change your vote -- Wisconsin is one of several states where you can change your early ballot if you think you've made a mistake," Trump said. "We'll make America great again."

The Republican nominee also encouraged voters in Michigan, Pennsylvania and nearby Minnesota who have already voted to "change your vote to Donald Trump."

Read More