The first wave of data from states like Florida and North Carolina shows preliminary signs that Mrs. Clinton was building a slight edge even before the revelation that Donald J. Trump had bragged about sexual assault roiled the race.
Democrats are requesting more absentee ballots in Florida than they were at this point in 2012, with increases of 50 percent in the heavily Hispanic areas around Miami and Orlando. In North Carolina, where Mitt Romney built enough of a lead in early voting four years ago to edge out a victory over President Obama, Democrats are requesting mail-in ballots in larger numbers than in 2012, while Republicans' participation is declining.
These results will have more impact than ever this year, as record numbers of people are expected to cast their votes early. So many Americans will have voted by Election Day — more than 40 percent in swing states, according to the Clinton campaign — that the winner could be known before November.
But despite Mrs. Clinton's growing lead in the polls, her campaign to defeat Donald J. Trump with early get-out-the-vote efforts is advancing along a tenuous path.
Nowhere is the trench warfare over registration and early voting closer or more vital than in Florida. In a sign of how thin the margin of victory could be, the state Democratic Party sued the Republican governor, Rick Scott, to extend Tuesday's voter registration deadline because of the disruptions caused last week by Hurricane Matthew. On Monday, a federal judge agreed to push back the deadline by one day and set a hearing for Wednesday to consider delaying it further.
Barring a huge shake-up in other swing states, Mr. Trump will lose the race if he loses Florida. Florida Republicans have significantly narrowed a voter registration gap with Democrats, which stood at more than half a million people four years ago. As of mid-September, it had shrunk to just over 274,000. Republicans were also increasing their numbers in North Carolina, Nevada and Pennsylvania.
"We've really moved the margins in so many of these states," said Chris Young, the national field director for the Republican National Committee. "And the reality is the Democrats are out of time when it comes to voter registration. In a majority of states, they've got a week, maybe two, tops."
Typically, the last weeks before the voter registration deadline are the most fruitful for Democrats. And Robby Mook, Mrs. Clinton's campaign manager, said he was confident of where they stood in Florida and other swing states.
"We are literally in the midst of the highest peak in voter registration for our campaign," he said last week during a conference call with reporters, in which he called on Mr. Scott to extend the deadline because of the storm. "President Obama definitely saw the same thing back in 2012. So we know you will see those voter rolls change, but it will take a little time."
Vote-by-mail requests among Hispanics in Florida, Mr. Mook added, are up 77 percent. And voter registration data there backs up his assertion that they are breaking for the Democratic Party in unprecedented numbers. Since Jan. 1, just 16 percent of new Hispanic voters registered as Republicans. That is down significantly compared with Hispanic voters who registered before 2013: 28 percent of them registered as Republicans, according to Daniel A. Smith, a political science professor at the University of Florida.
The Clinton campaign has undertaken an ambitious effort to find likely supporters, identifying and modeling the voting behavior of every voter in the swing states.
NewYork Times Reports