WASHINGTON — If Donald Trump or Hillary Clinton scored a high note or commited a blunder in Sunday’s presidential debate, millions of voters can respond almost immediately. They can fill out a mail-in ballot right away or head to a polling location the next day.

Early voting is on the rise in America. More than 45 million people are expected to vote before Election Day, Nov. 8, either by mail-in ballots or going to early-voting stations. Advance voting is underway in nearly half the 50 states, with more to follow. At least 403,000 people have voted already, according to data compiled by The Associated Press.

The Clinton campaign is pinning much of its strategy on the early vote, hoping to lock in less-reliable voters. Campaign manager Robby Mook pointed this past week to North Carolina, Florida and Nevada as states where the campaign hopes to build an “insurmountable lead” before Nov. 8 on the way to the 270 electoral votes needed to win.

Early voting may offer some early clues about the race. There are encouraging signs for Clinton in North Carolina, and judging by ballot requests, the first presidential debate seemed to help Democrats more than Republicans in pockets of the U.S.

But Clinton’s push for mail-in voting in Florida could be hurt by Hurricane Matthew, which struck just as ballots were being mailed to voters.

The Trump campaign isn’t copying the Democrats’ expensive, labor-intensive efforts to promote early voting. Instead, it’s leaning heavily on the Republican National Committee for its get-out-the-vote-effort and counting on mass rallies and big television audiences to spur early voting.