@snood,
Well I am a registered Democrat after all.
Michigan usually has open primaries, and people are usually free to vote in whichever primary they want (although they can't vote in both).
I often cross party lines and vote in whatever primary I can make a difference in. Or if the best candidate overall is a Republican I will cross over and vote for them in the primary.
In this case there isn't much of a difference that I could make in either primary. The Republican primary is going to go to Trump no matter what, so there was no point in voting in the Republican primary.
If the Sanders/Biden choice is really between two equally bad choices, then my choice there is pointless as well.
But there is a small chance that Sanders is less-bad on guns.
I considered skipping both primaries and just voting on the local millages. But since there is no way that Sanders could be any worse than Biden on guns, voting for him can't do any harm even if they are equally as bad.