Before you do that, look at the rest of the races. Especially if you are in a state with jungle primaries. There may be lower office races, or especially local races where republicans could have a chance (even NY has republicans). Your one vote will probably not make a difference for the presidential primary, but it very well could be the difference in having a good candidate for a local school board or council, and having a RINO. Some of those races are won by a very small number of votes. There have even been coin flips to break a tie.