If you're planning to vote in California's primary on Tuesday (and I hope you are!), and you're registered as "Decline to State" - DTS - then you need to know something about how the process actually works so that you can actually vote for a Democratic presidential candidate.
Happily, the Courage Campaign and Handsome Donkey have produced a great, hilarious instructional video that explains what you must do:
Basically, if you are registered as DTS - as nearly 20% of California voters now are - you have to ask for a Democratic Party ballot when you get to your polling place on Tuesday. Otherwise, if you don't ask, you'll be handed a ballot that doesn't list the Democratic nominees.
As Rick Jacobs explains in the comments, in our 2004 primary some 500,000 DTS voters didn't cast a vote for president even though they voted on the other ballot measures. We've got to improve these numbers this year.
Are you a registered Democrat? If so, great, you'll have no problem. But you almost certainly have friends, family members, even a fiancee (I do!) who is registered as DTS. Chances are they aren't aware of this important step that they have to take. Send them the link to this video and the information about DTS voters to ensure that their vote will be counted on Tuesday!
If you are a vote-by-mail DTS voter, you can still vote in the Democratic primary. What you need to do is take your ballot that you received in the mail without having filled it out yet (see comments below) and ask a poll worker to exchange it for a Democratic Party ballot.
Some poll workers may not have been fully trained about this, and may deny you a Democratic Party ballot. If this happens, ask to fill out a provisional ballot.
More info can be found at the CA Secretary of State's website and at the Courage Campaign.
Note: Republicans don't allow DTS voters to vote in their primaries. Something about wanting their ultra-right party membership to make the decisions instead. Go figure. Besides, you didn't want to vote in their primary anyway.
It doesn't matter which Democrat you vote for - just make sure you and your friends know what they have to do to make your votes count. All you have to do is ask.