NPR:

An extraordinarily high number of ballots — more than 550,000 — have been rejected in this year’s presidential primaries, according to a new analysis by NPR.

That’s far more than the 318,728 ballots rejected in the 2016 general election and has raised alarms about what might happen in November when tens of millions of more voters are expected to cast their ballots by mail, many for the first time.

Election experts said first-time absentee voters are much more likely to make the kinds of mistakes that lead to rejected ballots. Studies also show that voters of color and young voters are more likely than others to have their ballots not count.

Most absentee or mail-in ballots are rejected because required signatures are missing or don’t match the one on record, or because the ballot arrives too late.