When you're voting in the presidential primary, you're actually voting for the delegates who will go to the convention.
Especially this year, where both parties are running people who are old enough for untoward events to happen suddenly, you want to send delegates whose second choice would be acceptable to you. (And in some states, if don't vote explicitly for delegates, your vote has no effect.)
@AlphaCentauri If they a voting record always look at that.
If you get a mail ballot, you can take the time to research them. Delegates' social media pages can be very instructive.