Though Democrats can take solace from the fact that their large organizational advantage has supplied a cushion when they need it most, the race is still exceedingly close. And the latest eruption in the email affair still threatens to turn many voters against Mrs. Clinton - and put Democrats in lower-level contests on the defensive - just when it appeared Mr. Trump and other Republican candidates were falling out of contention.
"We cannot get distracted by all the noise in the political environment," Mrs. Clinton urged voters on Sunday in Fort Lauderdale, Fla. reminding them that three million Floridians had already voted. "We've got to stay focused."
While the early-voting numbers appear strong for Mrs. Clinton, there were signs of weakness over the weekend, especially among African-Americans in North Carolina, where the turnout as of Saturday night showed that they had not voted at their 2012 levels so far.
Among both supporters and critics of Mrs. Clinton, early returns suggest the latest uproar has changed few minds, despite seeming to break through the campaign din. In interviews with more than three dozen voters in three early-voting states - Colorado, Florida and North Carolina - most had at least a passing familiarity with the email developments but said the news had no bearing on their decisions at the ballot box.
"Enough is enough with the emails," said Marialuisa Glait, 33, of Miami, holding her 2-year-old son, Joaquin, after voting for Mrs. Clinton.
Fernando Gonzales, 26, another early Clinton voter in Miami, said this consistently implausible election season had long ago deadened his nerves to shock.
"The October surprise doesn't mean anything," he said. "The bar's been lowered so much, you can't lower it any more."
Because of a large advantage in mail-in ballots, registered Republicans in Florida have the thinnest of edges over registered Democrats in votes cast so far - less than a percentage point. But that advantage has diminished as in-person voting has begun and is smaller than the lead Republicans had at this point four years ago. The Democratic gains owe in large part to high turnout among Hispanics, who have typically waited until much later to vote.
"Hispanics are outperforming," said Daniel A. Smith, a political science professor at the University of Florida who has been analyzing demographic data about early turnout that the state is required to collect. "They are more engaged in this election cycle, and more are voting earlier than we saw in 2012."
In North Carolina, Democrats have a wide lead in the number of ballots cast so far, with 43 percent to Republicans' 31 percent. But because the state significantly curtailed early voting, Democrats have lagged behind their 2012 participation rate, while Republicans are running ahead. As more polling places open, Democrats are catching up to their 2012 rates.
"They keep eating that deficit away," said J. Michael Bitzer, a professor of political science at Catawba College.
Mr. Bitzer said there should be other warning signs for Mr. Trump: Women have cast 56 percent of the votes in North Carolina so far, and rural voters are slightly behind their 2012 participation rates.
The nagging question for Mrs. Clinton is whether Democrats can bolster black turnout, which is down 17 percent so far, Mr. Bitzer said. "That's the biggest concern for her," he added.
Democrats are also beating Republicans so far in Colorado and Nevada, where Mr. Trump held rallies over the weekend and continued to question the integrity of the voting process, even as he implored his supporters to send in their ballots.
"We've got a lot of people watching the people that collect the ballots," Mr. Trump said on Saturday in Golden, Colo. Thirty-nine percent of the ballots received in Colorado so far have been from registered Democrats, 35 percent from Republicans. Democrats overcame Republicans' longstanding registration advantage there this year, a worrisome sign for Mr. Trump and his party.
In Nevada, where Mr. Trump campaigned on Sunday, Democrats were voting at a rate that exceeded Republicans' participation by seven percentage points. Crucially, in bellwether Washoe County, which includes Reno, more Democrats had voted as of late Saturday.
Mrs. Clinton and her allies are directing their campaign visits almost exclusively to early-voting states: On Saturday, Mrs. Clinton appeared with Jennifer Lopez at a concert in Miami. Former President Bill Clinton appeared on Sunday in North Carolina, and Mrs. Clinton was to campaign on Monday in Ohio.
Her goal, aides said, is to build an advantage that Mr. Trump cannot overcome even if he wins the majority of votes cast on Election Day.
By contrast, Mr. Trump's minimal organizing has essentially left voter mobilization efforts to the Republican National Committee. Officials there expressed confidence despite having a far larger role than they had anticipated.
"We're seeing some very positive metrics," said Chris Carr, the committee's political director. "I would say we're running at parity or ahead of the Clinton campaign."
Both campaigns have embarked on an intense chase for those among their supporters who are least likely to vote - people who could hold the key to the election. If these people turn out, then early voting actually adds to Mrs. Clinton's or Mr. Trump's vote totals. Otherwise the effect of early voting would be relatively meaningless: People would have voted anyway, just at a different time
Clinton aides said they had created a battleground-state model that scores voters from 1 to 100 based on factors such as their likelihood of voting and their susceptibility to advertising. So far, among those the Clinton campaign sees as least likely to turn out - people who have skipped nonpresidential elections - Democrats are voting in far greater numbers than Republicans in both North Carolina and Nevada, and in slightly larger numbers in Arizona.
The F.B.I.'s disclosure on Friday, rather than changing many minds, seemed to largely confirm the sentiments of people who were voting early.
"If I was a Democrat, I'd certainly be questioning my vote," said Steve Flynn, a 65-year-old retired construction worker who lives outside Denver and voted for Mr. Trump.
But his daughter-in-law, Whitney Dorman, said she and her husband would still be likely to cast their votes for Mrs. Clinton.
"I really don't care," said Ms. Dorman, 31, a graphic designer. "Is she in people's pockets? Sure, why not."
T.J. Blazer, 44, who said he had voted for Mr. Trump in St. Petersburg, Fla., said he was taken aback by what he viewed as an admission by the F.B.I. that it had mishandled Mrs. Clinton's case.
At least as disorienting, he said, was the return of Anthony D. Weiner to his television - a turn that seemed to confirm everything that was already so odd about this election.
"Next thing I know, his picture popped up," he said. "Where did he come from?"