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In states where voting by mail is on the rise, there's a wonky reason why officials may be slower to report midterm results on election night.

Before mail-in ballots can be counted, they have to go through a process sometimes referred to as "pre-canvassing."

It can include checking voters' signatures on the return envelopes, opening the envelopes, taking out the ballots, flattening and then grouping them into stacks ready for scanning.

These seemingly mundane but critical steps can take hours or days to finish depending on how many people vote by mail. The Bipartisan Policy Center has recommended allotting at least seven days before Election Day for this process.

Some states, however, have election laws in place that do not allow pre-canvassing to begin until that last day of voting. That includes the key swing states of Wisconsin and Pennsylvania, where prep work cannot start until 7 a.m. local time on Election Day.

This restriction puts those states' election officials at a disadvantage in terms of turnaround times — especially when compared to states where both pre-canvassing and counting are allowed to start before Election Day.

"Election workers must be given a reasonable amount of time to do their jobs thoroughly. Unofficial results will be available within a few days of the election, and it's critically important for everyone to understand that this delay does not mean anything nefarious is happening. An accurate count of all eligible votes is paramount, and it cannot be rushed," Pennsylvania's acting secretary of state, Leigh Chapman, said Monday in a statement.

There have been multiple proposals to move up Pennsylvania's legal start time for pre-canvassing mail ballots. But the state's Republican-controlled legislature and its Democratic governor could not agree on a legislative package that would include pre-canvassing changes and GOP state lawmakers did not advance more tightly focused bills that were introduced before the midterm elections.

A new election law in Michigan, however, has widened the window for processing mail ballots in some areas of that swing state. Communities with at least 10,000 residents can now start pre-canvassing two days before Election Day, although some election officials said this law, which was passed last month, came too late, as they had already finalized their staffing and other plans for the midterms.

Still, with close to 2 million mail-in ballots requested in Michigan as of last week — and more than 1.4 million in Pennsylvania — election officials in these closely watched states will have plenty of work left to do after the ballots are processed and ready for counting.

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