WASHINGTON (AP) — Pennsylvania voters are almost sure to play a pivotal role in the Nov. 5 general election, with control of the White House and both chambers of Congress and the state Legislature in the balance.

With its 19 electoral votes, the commonwealth is the largest prize among the battleground states and an important piece of both campaigns’ path to victory. Both Democratic Vice President Kamala Harris and Republican former President Donald Trump have made frequent visits to the state since becoming their parties’ nominees, including for their sole debate in Philadelphia in September.

Pennsylvania was one of three “blue wall” swing states that went narrowly for Trump in 2016 after almost 30 years of voting for Democratic presidential candidates; the others were Michigan and Wisconsin. Four years later, Democrat Joe Biden won all three states back for Democrats with a margin in Pennsylvania of about 80,000 votes out of more than 6.9 million votes cast. The states remain key electoral prizes this year.

In the U.S. Senate race, Democratic incumbent Bob Casey seeks a fourth term against Republican Dave McCormick. Casey, the son and namesake of a former two-term governor, has one of the most recognizable names in state politics but this year he faces what has shaped up to be the toughest race of his Senate career. The seat is critical to Democratic hopes of keeping control of the narrowly divided chamber. McCormick, a former hedge fund CEO and Army combat veteran, ran for Pennsylvania’s other U.S. Senate seat in 2022 but lost the GOP nomination to Mehmet Oz, who went on to lose to Democrat John Fetterman.

Further down the ballot, a handful of competitive races could play a role in determining control of the U.S. House. In the 7th Congressional District, Democratic U.S. Rep. Susan Wild seeks a fourth full term against Republican Ryan Mackenzie. In the neighboring 8th Congressional District, Democratic U.S. Rep. Matt Cartwright seeks a seventh term against Republican Robert Bresnahan. The 7th District in eastern Pennsylvania narrowly went for Biden in 2020, while voters in the 8th District, which includes Biden’s hometown of Scranton, preferred Trump.

In the race to control the state Legislature, Democrats are defending the razor-thin state House majority they won in 2022 for the first time in 12 years and have since successfully defended in several special elections. All 203 state House seats and half the 50 state Senate seats are up for election this year. Republicans have a majority in the state Senate.

Here’s a look at what to expect in the 2024 election in Pennsylvania:

Election Day

Nov. 5.

Poll closing time

8 p.m. ET.

Presidential electoral votes

19 awarded to statewide winner.

Key races and candidates

President: Harris (D) vs. Trump (R) vs. Chase Oliver (Libertarian) vs. Jill Stein (Green).

U.S. Senate: Casey (D) vs. McCormick (R) and three others.

7th Congressional District: Wild (D) vs. Mackenzie (D).

8th Congressional District: Cartwright (D) vs. Bresnahan (R).

Other races of interest

U.S. House, Attorney General, Auditor General, Treasurer, state Senate and state House.

Decision Notes

Several factors contribute to a relatively slow vote counting process in Pennsylvania. Under Pennsylvania law, elections officials must wait until 7 a.m. ET on Election Day before they can begin to process ballots cast by mail and prepare them to be counted. The actual tabulation of mail ballots cannot begin until after polls have closed. Because of the overall volume of mail ballots — they comprised almost a quarter of the total vote in the 2022 midterm elections — and the varying amounts of time it takes the state’s 67 counties to tally these votes, determining a winner in a highly competitive race could take several days, as it did in the 2020 presidential election.

The first vote results reported after polls close are expected to come from mail ballots. Results from later in the night are expected to be a mix of mail votes and votes cast in person on Election Day. Once the vote counting stretches into the day after Election Day and beyond, the vote results are once again expected to come mostly from mail ballots.

Overall, votes cast by mail have tended to favor Democrats, ever since the issue of early and mail voting became highly politicized during the 2020 election. This means the Democratic candidate in a competitive contest could take an early lead in the vote count in the initial vote reports after polls close, even though the race may tighten considerably as more votes are tabulated.

In 2020, Biden took an early, temporary lead after mail voting results began to be released shortly after polls closed at 8 p.m. ET. By about 10 p.m. ET, Trump took the lead as more results from Election Day voting were released. By early Wednesday morning, Trump led Biden by nearly 700,000 votes, but that lead would gradually shrink as more mail ballots were tabulated. Biden eventually retook the lead by Friday morning.

The suburban “collar counties” around Philadelphia are key battlegrounds and have been trending toward Democrats in recent years. In statewide elections, Republican candidates tend to win overwhelmingly in rural areas statewide, while Democrats rely on lopsided support in Philadelphia and Pittsburgh.

Erie and Northampton counties on opposite sides of the state may also hold clues on election night. They are two of only 10 counties across all the presidential battlegrounds that voted for Trump in 2016 and flipped to Biden in 2020.

The Associated Press doesn’t make projections and will declare a winner only when it has determined there is no scenario that would allow the trailing candidates to close the gap. If a race hasn’t been called, the AP will continue to cover any newsworthy developments, like candidate concessions or declarations of victory. In doing so, the AP will make clear it hasn’t declared a winner and explain why.

In Pennsylvania, races with a vote margin of 0.5 percentage points or less are subject to an automatic recount. The AP may declare a winner in a race that is eligible for a recount if it can determine the lead is too large for a recount or legal challenge to change the outcome.

Past presidential results

2020: Biden (D) 50%, Trump (R) 49%, AP race call: Saturday, Nov. 7, 2020, 11:25 a.m. ET.

Voter registration and turnout

Registered voters: 9,036,833 (as of Oct. 14, 2024). About 44% Democrats, about 40% Republicans, about 12% unaffiliated.

Voter turnout in 2020 presidential election: 76% of registered voters.

Pre-Election Day voting

Votes cast before Election Day 2020: about 38% of the total vote.

Votes cast before Election Day 2022: about 23% of the total vote.

Votes cast before Election Day 2024: See AP Advance Vote tracker.

How long does vote-counting take?

First votes reported, Nov. 3, 2020: 8:09 p.m. ET.

By midnight ET: about 54% of total votes cast were reported.

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Associated Press writers Hannah Fingerhut, Jonathan Poet and Maya Sweedler contributed to this report.

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Read more about how U.S. elections work at Explaining Election 2024, a series from The Associated Press aimed at helping make sense of the American democracy. The AP receives support from several private foundations to enhance its explanatory coverage of elections and democracy. See more about AP’s democracy initiative here. The AP is solely responsible for all content.