Election workers across Pennsylvania chipped away at more than 1 million uncounted mail ballots Wednesday as the nation awaited results in a presidential battleground whose trove of 20 electoral votes remained the largest prize yet to be called for President Donald Trump or native son Joe Biden.

Amid legal action from the Trump campaign that Democratic Gov. Tom Wolf condemned as “disgraceful," workers in counting rooms throughout the state processed unending streams of paper ballots — removing them from their envelopes, flattening them and feeding them into scanners — as Pennsylvania gradually counted a vote that could prove decisive.

Biden came within six electoral votes of winning the presidency Wednesday evening when he won Michigan. A win in any state yet uncalled — except for Alaska — would be enough to end Trump’s tenure in the White House.

State officials counseled patience even as they said a winner might not be known for days.

“The delay that we’re seeing is a sign that the system is working,” said Wolf, pledging that all of the votes were “going to be counted accurately and they’re going to be counted fully.” He said that “every Pennsylvanian can have confidence in the outcome of this election.”

The Trump campaign said it sued to temporarily stop the vote count in Pennsylvania over what it called a lack of transparency, demanding better access for campaign observers. In one lawsuit, it complained one of its representatives was kept so far away that he could not see the writing on mail-in ballots that were being opened and processed in Philadelphia. A judge dismissed it, saying that poll watchers are directed to observe, not audit. The campaign is appealing.

In another lawsuit, the Trump campaign disputed the state's guidance over the timeline for voters to provide proof of identification for a mail-in or absentee ballot that arrives within three days after polls close.

The campaign also sought to intervene in an ongoing Supreme Court case over late-arriving and potentially crucial mail-in ballots. Separately, Republicans accused the Wolf administration of changing vote-counting rules on the fly, mounting several court challenges that remained pending Wednesday.

“Bad things are happening in Pennsylvania,” Trump's deputy campaign manager, Justin Clark, said in a statement.

Wolf accused Republicans of seeking to undermine confidence in the election results, and his elections chief said the state acted legally and properly to ensure a complete and accurate count. More than 2.6 million mail-in ballots were cast, and there has been no report of fraud or any other problem with the accuracy of the count.

Condemning the Trump campaign, Wolf said: “Our election officials at the state and local level should be free to do their jobs without intimidation or attacks. These attempts to subvert the democratic process are disgraceful."

Lisa Schaefer, executive director of the County Commissioners Association of Pennsylvania, said she had been expecting the Trump campaign to mount a legal challenge in the state, but she defended election officials.

“I still believe that our counties are following the proper processes and protocols to ensure a fair and accurate count at this point,” she said. “We’re going to do the best that we can to deliver an accurate result.”

The ballot deluge was the result of a a new state law that greatly expanded the ability of Pennsylvania residents to vote by mail. The counties were not allowed to begin processing those votes until Election Day, meaning it could take days before a winner emerges. Pennsylvania offered the biggest haul of electoral votes of any state yet to be called by The Associated Press.

Some of Pennsylvania’s most heavily populated locales, including Philadelphia and suburban counties like Montgomery, Chester, Bucks and Delaware — all seen as fertile territory for Biden — were tabulating mailed votes around the clock. Several GOP-run counties where Trump dominated in 2016, including York, Cumberland, Butler and Westmoreland, also had tens of thousands of votes left to count.

Philadelphia showed live video of workers in yellow and orange safety vests preparing ballots to be scanned.

“Counting votes cast by mail, if you’re going to do it right and you’re going to do it accurately — because there’s no other choice — takes a little bit of time. So I know that’s very frustrating,” City Commissioner Al Schmidt said Wednesday, adding that “it’s more important than we do it right than meet artificial deadlines.”

Allegheny County, where Pittsburgh is, stored ballots in a locked cage under surveillance during an overnight pause in the count. Ballot processing resumed Wednesday.

Challenging 93 mail-in ballots in the Philadelphia suburbs, the GOP said officials in Montgomery County had unfairly given voters a chance to fix technical mistakes on their mail-in ballots before Election Day, something not all counties allow. Ballot scanning machines had rejected about 2,700 mail-in ballots missing a signature or an inner secrecy envelope, and 93 of those voters “cured” or fixed the mistakes.

“I don’t understand how the integrity of the election was jeopardized,” U.S. District Judge Timothy Savage said, grilling GOP lawyer Thomas Breth.

Breth complained that many Republican-leaning counties in the state don’t follow the same practice, and said it’s not expressly allowed under the state election code.

But Michele Hangley, arguing for county officials in the Democratic stronghold, said the standard shouldn’t be “the lowest effort made” by any one county.

Savage did not plan to rule before Friday.

Republicans have also challenged a state Supreme Court ruling that orders counties to count mailed ballots arriving up to three days after Election Day, so long as they were mailed by Election Day.

Pennsylvania’s secretary of state, Kathy Boockvar, has told counties to segregate late-arriving ballots because of the ongoing GOP litigation, but to count them in the meantime.

Republican-controlled Lancaster County has refused, saying they had no way to count late-arriving ballots and then separate them from the overall tally if those ballots are later thrown out by the U.S. Supreme Court. The county said it received 523 mailed ballots on Wednesday.

“The problem for us, as we have been told by our elections office staff, is that once you scan these in, you can’t basically remove them” from the count, said Josh Parsons, chair of the Lancaster County board of commissioners.

He said state elections officials advised Lancaster County to buy software that would allow the county to extract the votes, but Parsons said it wasn’t a realistic solution given the timing.

Boockvar pushed back, saying it is “absolutely feasible and not even challenging.” She said she expected compliance.

Several other counties have also delayed the counting of late-arriving ballots, including Beaver, York and Allegheny.

“We are preparing as if we may need to count them at any time and at that point, if that is the decision, we will act accordingly," York County spokesperson Mark Walters said.

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Rubinkam reported from northeastern Pennsylvania. Associated Press reporters Maryclaire Dale in Philadelphia, Marc Levy in Harrisburg and Anthony Anthony Izaguirre in Lindenhurst, New York, contributed to this report.

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Find AP’s full election coverage at APNews.com/Election2020.