WASHINGTON — Donald Trump’s supporters may hope that last week’s FBI revelation about the Hillary Clinton e-mail investigation might give the Republican’s campaign a boost. But it’s already too late for Trump to win over around a fifth of American voters, including many of the most coveted ones in battleground states.

Tens of millions of voters had already cast ballots before news broke Friday that the FBI was examining newly discovered e-mails that might be pertinent to the dormant investigation of Clinton’s use of a private e-mail server.

In critical states such as Florida, Nevada and Colorado, one-third or more of the expected ballots have already been cast. The breakdown of those voters by party affiliation, race and other factors points to an advantage for Clinton. That will make it more difficult for Trump to capitalize on the FBI news.

Overall, early voting — by mail and at polling stations — is under way in 37 states.

At least 24.6 million votes have been cast, far higher than the rate in 2012, according to Associated Press data. That represents nearly 20 percent of the total votes expected nationwide, if turnout is similar to 2012. In all, more than 46 million people — or as much as 40 percent of the electorate — are expected to vote before Election Day, Nov. 8.

In Florida, more than 3.7 million early ballots have been cast, or nearly half the total votes cast there in 2012. Democratic ballots are now virtually tied with those cast by registered Republicans, each with about 40 percent. Democrats have kept it close during mail balloting, when Republicans historically have done better. GOP analysts say Democrats now hold the advantage. Barack Obama won the state in 2008 and 2012. It’s a must-win state for Trump.