(The Center Square) – The majority of mail-in ballots requested in Pennsylvania have been returned as of 8 a.m. Monday.

Of the 2.2 million issued, the Department of State is in receipt of 1.8 million, or 81.4%, according to its daily report. By party, Democrats have mailed in 83.1% of the 1.2 million requested; Republicans 82.1% out of 715,287; and unaffiliated or other third parties at 72.7% out of 282,162.

That leaves roughly 408,000 ballots unaccounted for heading into Election Day. Votes received after 8 p.m. on Tuesday will not be counted. Postmarks will not suffice.

More than 9 million residents are registered to vote in Pennsylvania, where all signs point to a tight race that could deliver the White House to either candidate.

The commonwealth’s 19 electoral college votes lead the pack of seven swing states, including North Carolina and Georgia at 16; Michigan 15; Arizona 11; Wisconsin 10; and Nevada at six.

President Joe Biden’s 2020 win in Pennsylvania against incumbent Donald Trump came in at less than 82,000 votes. In 2016, Democratic challenger and former Secretary of State Hillary Clinton lost the state by roughly 40,000 votes.

Since Al Gore (2000) and John Kerry (2004) won the state, Pennsylvania's electoral college votes have gone to the eventual president every cycle.

Vice President Kamala Harris’ rally schedule suggests the Democrats hope to hold onto Biden’s margin on Tuesday. Her campaign will spend all day crisscrossing the state to Pittsburgh, Philadelphia, Allentown and Scranton.

Trump, meanwhile, will hit Pittsburgh and Reading as the two candidates – polling a dead heat, according to the most recent RealClear average – spend the eve of the campaign vying for the affections of Pennsylvania voters.

Meanwhile, county election offices arguably face a more grueling schedule. Understaffed and overloaded with mail-in ballot processing duties, errors and accusations of fraud have already made headlines.

In Lancaster, York and Monroe counties, workers have intercepted thousands of suspicious voter registrations, many of which are linked to a charity canvassing operation tied to a liberal super political action committee.

The Pennsylvania Democratic Party also sued the Erie County Board of Elections for mail-in ballot errors impacting up to 20,000 voters.

And across the state in Bucks County, a suburb of Philadelphia, Trump’s campaign filed a legal challenge against election officials for alleged voter suppression. The action came after workers told residents that requested mail-in ballots could no longer be submitted on the spot – a choice that slowed down the process and created long lines outside of the office.