The race could hinge on Georgia, Arizona and Nevada because if Biden is declared the winner in any two of those three states, he will surpass the needed 270 electoral college votes.
Yet a win in Pennsylvania by Biden will single-handedly hand him the White House. It remains unclear how long it will take for counties across the state, including Philadelphia, to finish tallying their mail-in ballots.
The slow grind toward counting all 2.6 million mail-in votes has been expected for months because the Republican-controlled state legislature refused to change the election code to allow for counting of mail-in ballots before Nov. 3.
Election officials across the state expect the vast majority of the votes to be counted by Friday. In just Philadelphia, for instance, 120,000 votes still need to be counted.
A county commissioner there said Wednesday that they can count about 10,000 votes per hour.