It is not an open primary — registered Republicans only.
Someone posted a thread about it the other day.
This should help Sen Cruz.
I think there is a real possibility that no one gets to 1237 and then it's going to be a question of who can get there on the 2nd or 3rd ballot. A contested convention favors Sen Cruz, after all the vitriol from Trump I can't imagine anyone crossing over to join him after the 1st ballot.