And if that's the case, then let's have a look at what the Wisconsin Constitution has to say about speech:
no laws shall be passed to restrain or abridge the liberty of speech
What about the big one, the U.S. Constitution?
Congress shall make no law... abridging the freedom of speech
Thanks to Gitlow v. New York, we know that the Bill of Rights extends to all the states, as well.
So the fundamental question remains, is voting a form of speech just like making a monetary contribution to a political campaign is speech? Better put, is it expression?