Supporters of Hillary Clinton attend a rally in Harrisburg, Pa., on Oct. 4. (Melina Mara/The Washington Post)

Democratic presidential nominee Hillary Clinton could run up an “insurmountable lead” in Florida, North Carolina and Nevada ahead of Election Day because of early voting, effectively deciding the outcome of those battleground states, Clinton campaign manager Robby Mook said Thursday.

Democrats expect that at least 40 percent of votes will be cast ahead of Nov. 8 in battleground states that allow early voting, Mook said during a conference call with reporters. He claimed that early indications in crucial Florida and Ohio are positive for Democrats. Clinton leads Republican Donald Trump in Florida by 2.4 percentage points in the RealClearPolitics average of recent polls, and trails Trump in Ohio by the same margin.

Clinton's deficit in Ohio is shrinking, which Democrats attribute largely to momentum from her performance in the first presidential debate.

Clinton's campaign is also pressuring Florida election officials to extend an Oct. 11 deadline to register to vote because of the disruption expected from Hurricane Matthew.

“Our hope would be that a little more time will be given,” Mook said. “We certainly expect that the governor and local officials will make that possible.”

Florida Gov. Rick Scott, a Republican, had said  Wednesday that the hurricane won't have an impact on voting, citing ample opportunities for early voting in the state.

Clinton’s campaign suspended election advertising on the Weather Channel in Florida on Thursday after  Republican criticism that she was profiting from the Category 4 hurricane, which has prompted evacuation recommendations in Florida and other states.

“Since the storm has clearly become very serious, we have asked the Weather Channel to roll back that buy until the storm is concluded,” Mook said. “We don’t think that the voters in Florida need this election to get mixed up in their efforts to get information on this storm.”

Democrats are not likely to overtake Republicans in the number of people who vote by mail in Florida, but “are expecting to close that gap that they have historically had,” Mook claimed.

“Knowing that President Obama won the state in 2012 and knowing that we believe we will actually proportionally get more votes than he did through vote by mail, we think that's a very encouraging sign,” Mook said.

The Republican National Committee claims a strong early showing in early voting in Florida, in keeping with a historic Republican advantage there, and disputes the notion that this year will somehow be different.

Both Democrats and Republicans are predicting success from a record mail-in vote in Florida this year. Mook noted that some 2.7 million Florida residents have requested to vote by mail, compared with about 1.8 million at the same time in 2012.

He claimed that Democrats are now “winning” the daily by-party tabulation of mail-in ballot requests “on most days.” He claims an advantage for Democrats in a 77 percent increase among Hispanics in mail-in ballot requests.

Elsewhere, Mook said that twice as many Democrats as Republicans are voting early in person in Iowa since the option became available last week, and he claimed the momentum in Ohio, where heavily Democratic Cuyahoga County, which includes Cleveland, accounts for one in six of the more than 950,000 absentee ballots received.