The recount underway in Pennsylvania’s U.S. Senate race marks the end of a chaotic post-election period that has become the latest example of how disputed election rules can expose weak points in a core function of American democracy.

The Pennsylvania Supreme Court on Monday ordered all 67 counties to comply with the commonwealth's existing Election Code and not include in tabulations, including the U.S. Senate recount, any mail-in ballots cast with dating errors on the outer return envelope.

These counties were ordered to not count illegal ballots after election officials voted to count ballots missing dates — in other words, ballots that did not comply with require

The Keystone State's top court reaffirmed that certain mail-in ballots cannot be counted, in a blow to certain Democrat-led counties.