(CNN) The 2020 presidential election looked like it was going to feature record turnout. Voters in 2018 turned in historic numbers , and polling indicated that voter excitement was high heading into 2020. Voter enthusiasm remains high, but limited evidence from Tuesday's primary elections suggests that the coronavirus pandemic may cause a drop in turnout in November if voting by mail is not made an option for voters.

Any of these examples individually could be dismissed. But together, Arizona Florida and Illinois make a fairly compelling case that the coronavirus pandemic could keep turnout down in November, if people fear going out and standing in lines with other people.

Illinois was the one state that voted this past Tuesday that does not make extensive use of early voting or voting by mail. Perhaps it's no surprise then that turnout was lower in Illinois than it was four years ago. Only about 1.5 million people turned out to vote in Illinois' Democratic primary. Four years ago, a little over 2 million people voted

That's a turnout drop of 25%. Taking into account the change in the number of eligible voters, as compiled by Michael McDonald of the United States Elections Project , the drop was still 25%. Illinois had the worst turnout relative to 2016 of any state that has voted so far.

Any downward shift in turnout is extremely unusual in the context of this primary season. Turnout was almost uniformly up this primary season in states where we could fairly compare rates (i.e. not counting states that moved from lower turnout caucuses to higher turnout primaries). Across all of these nearly 20 contests, turnout rose by around 20% no matter how you calculate it.

All but Oklahoma had seen its turnout rise. Oklahoma, of course, has a lot of registered Democrats who no longer identify as Democrats , but they're not allowed to vote in Republican primaries because of the state's election laws . And even there, the drop in turnout was less than half of that of Illinois.

Now, one could argue that turnout in Illinois was down because the Democratic primary had become uncompetitive. As I wrote more than a week ago , Joe Biden's got this.

But perhaps as instructive as what happened in Illinois is what occurred in Tuesday's other primaries in Arizona and Illinois.

Arizona has extensive in-person early voting and vote by mail. It's how most voters cast their ballots. With ballots still to be counted, Arizona's turnout is up from about 470,000 in 2016 to more than 530,000 in 2020. Arizona's rise in turnout is likely going to be near or slightly exceed the average this primary season once all the votes are counted.

Florida is an interesting in-between case and reinforces the point. It has a lot of in-person early voting and vote by mail, but not to the same extent as Arizona. Florida's turnout moved from 1.71 million in 2016 to 1.74 million in 2020, as of this writing. Taking into account how many more people are eligible to vote in Florida, there is, at this point, actually a 5% decline in turnout.

In other words, Florida didn't experience the same level of decline in turnout as Illinois, but it fell well below the turnout surge that most other states experienced.

What happened? Florida had a significantly higher turnout of votes cast before the day of the election. That led a lot of smart people to think turnout on the day of the election would be up . It didn't happen. Turnout was down significantly.