And officials in at least six counties in the Keystone State said they don't plan on counting mail-in ballots until after Election Day.
“The outcome of Tuesday’s election could well depend on Pennsylvania,” Secretary of the Commonwealth Kathy Boockvar said, according to the Philadelphia Inquirer.
“It is vitally important that the more than 3 million ballots cast by mail here be counted as soon as possible. The country will be looking to Pennsylvania for accurate and timely results," she told the newspaper.
More than 2.4 million mail ballots had been received in Pennsylvania as of Monday, officials said.
Nearly three times as many Pennsylvania Democrats (1.6 million) had voted by mail than Republicans, according to news reports.
So if only in-person results are reported on Election Day, it could look like a big win for President Donald Trump. But as mail ballots are counted, Trump's lead over former Vice President Joe Biden could narrow, political observers say.
Pennsylvania Gov. Tom Wolf announced on Twitter: "Pennsylvanians will not be intimidated. You can watch us count every vote and have a fair election."
Wolf warned voters to track Election Day results using reliable sources, and to "be on guard for disinformation."
The Pennsylvania counties of Beaver, Cumberland, Franklin, Greene, Juniata and Montour won’t begin reporting mail ballot results until Wednesday, although some election officials among that group said they would start processing them on Tuesday.
ALSO SEE: Philadelphia businesses board up their storefronts in case of post-Election Day disturbances.
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