We can find out who usually only votes in presidential years
Voter records are available to the public in many states, including names, addresses, party affiliation, and which elections each voter either participated in or failed to vote in. Political campaigns and parties use this information all the time. Our local Democratic committee purchases lists for our Town in New York from the Board of elections at a nominal cost, and then use that info for strategic targeting. But anyone can do it.
Perhaps more of us should be doing just that, preferably through a coordinated group effort with local Democrats, Indivisible, or other entities like that. I'm thinking a special effort should be made to identify registered Democrats who usually vote in Presidential election years but who tend to skip "off year" elections, including midterms. Hell some of us may even recognize the names of friends or acquaintances on those lists - who we can then make personal efforts to get them to the polls in November. Of course in some areas the fact that someone registers as a Democrat does not prove that they won't for a Trump loving Republican this fall, some caution is warranted.
We need to be doing all that we can to turn out as many Democratic voters as we can for this Fall's "off year" election. Here is a web site with some info regarding voting records that are available in different states:
https://publicrecords.onlinesearches.com/Voter-and-Elections-Information.htm