The Democratic race will come down to New York and California, both on March 7. Bradley has to win both. Bradley is favored in New York, watch California. If Bradley wins there too, Gore might still limp to victory with the help of Southern primaries, but don't count on it. If Bradley loses California, it's hard to see how he recovers.
Voters can vote for any candidate in any party primary.
But convention delegates will be apportioned only on the basis of the votes of registered party members. It's possible that Bradley could lose to Gore among Democrats but win when Independents and Republican ballots are added to his totals. The political consultants and pundits, that's who. If you can't stand pundits and consultants, root against the split result. But if it happens, it will be the metaphor for the tumultuous campaign no one predicted.