PHILADELPHIA – An unnerved yet energized America is voting with an urgency never seen before in the approach to a presidential election, as a record 90 million people have cast ballots despite an array of challenges: a pandemic, postal delays, long lines and court rulings that have tested faith in the country's electoral system.

In Texas and Hawaii, turnout has already exceeded the total vote from 2016, with days left for absentee ballots to be returned. Ten other states, including major battlegrounds like Georgia, Florida, North Carolina, Arizona and Nevada, have surpassed 80% of the turnout from the last presidential election. Overall, the early turnout has set the country on course to surpass 150 million votes for the first time in history.

The impact of this huge surge in turnout is one of the most unpredictable facets of the election, as strategists in both parties parse early returns for signs of any advantage. Joe Biden, the Democratic nominee, is counting on a strong early vote to help him flip states like Florida and Arizona that President Donald Trump carried in 2016. But Republicans are banking on their voters to turn out in bigger numbers on Election Day and deliver battleground wins, as they did in key states in 2016.

Though Democrats have maintained an edge in early turnout in nearly every state that has seen record participation, Republicans have been closing the gap. In Florida, for example, 40% of the ballots returned came from registered Democrats, and 37.9% from registered Republicans, and in heavily Democratic Miami-Dade County, registered Republicans are turning out at a slightly higher percentage than Democrats. Included in those returns are millions of ballots marked no party affiliation, with no indication whether Biden or Trump is leading.

A recent national poll by the New York Times and Siena College found that Republicans were more likely to vote on Election Day than to vote early, while Democrats showed a preference for voting early. Polls in Georgia, Iowa and other battleground states showed a similar trend.

As the nation enters one of the most consequential weeks for voting in recent years, with swaths of Americans nervous about whether their ballots will be received and counted and others determined to push through concerns about the virus to vote, officials across the country have been mounting a furious effort to shore up election systems that have been pushed to the brink. They are recruiting tens of thousands of additional poll workers, working around the clock to process ballots and keeping polling locations open late to accommodate long lines.

"I'm going to vote like my life depends on it," Marilyn Crowder, 60, said as she waited in a line a block long at Anna B. Day School in Northwest Philadelphia last week. The school, one of 17 early voting locations open for the first time in Philadelphia, has for weeks drawn lines of voters filing down the street.

For Crowder, a cancer survivor, the pandemic was a motivating factor, as well as what she saw as attempts by Republicans to make it harder to vote. "I personally felt powerless to do anything about it, except what I'm doing now," she said. "And now I'm making phone calls."

Les Bignell, 59, a sewer liner from West Allis, Wis., said he dropped his absentee ballot in the box at City Hall days earlier, casting a vote for Trump as he did in 2016. "I did it because of my bank account," he said. "When the lockdown first happened I lost a lot of money, but I got it all back already."

Never before in modern American politics has the electorate faced so many unknowns while so many Americans still pushed forward to cast their ballots through the mail and in person.

"The issues that are facing this country are generational," said Michael McDonald, a professor of political science at the University of Florida. He said the pandemic and the Black Lives Matter movement, coupled with the heightened political engagement since Trump's election, has produced a highly energized electorate.

"We wish we could care about other things in our lives, but right now, politics matter so much, and people are engaged," he said. Of course, non-battleground states, or states without a competitive statewide race, are unlikely to generate such intense voter interest, and early turnout can sometimes lag for reasons ranging from different start dates to disruptions from a hurricane or even wildfires.

Perhaps no state has seen a greater surge than Texas, a suddenly competitive state for Biden. More than 9 million voters had cast their ballots there as of Friday, despite restrictions ordered by Gov. Greg Abbott that limited ballot drop-off locations to one per county.

Raquel Gair Sutton, a former teacher from Arlington and a Democrat, said she always casts her ballot on the first day of early voting. This year, with her husband running for mayor, she waited 4 ½ hours to vote, beating her previous record by about three hours.

"I was blown away," said Sutton, whose husband, a local City Council member, has served as the election judge for their local precinct in Tarrant County. "I think it means good things for Biden, but we thought that four years ago. People are just ready for change."