New Jersey demands all vote with mail in ballots even if you go to a poll, if you can find one. Now MIT has noted:
In elections, every vote counts. Or should count. But a new study by an MIT professor indicates that in the 2016 U.S. general election, 4 percent of all mail-in ballots were not counted — about 1.4 million votes, or 1 percent of all votes cast, signaling a significant problem that could grow in 2020. The study quantifies the range of reasons for this, including late-arriving ballots, problems with ballot signatures and envelopes, and improperly marked ballots, among other things. “Mail ballots tend to have more mistakes on them,” says Charles Stewart, a professor in MIT’s Department of Political Science and author of a paper detailing the study, which looks at data from all 50 U.S. states.
Thus 4% is what we would expect in NJ or even more. 4% itself is a massive swing in votes and makes any election quite suspect. In addition in NJ one has no idea if one's vote is rejected. Moreover massive mail in voting especially in Democrat states may or may not make a difference in Presidential but will do so in Congressional.