Zenie, On the surface, closed primaries would seem to solve the problem of "jamming" a viable candidate. But there are a few problems with them, as I see it. One is that last minute developments could prevent members of an opposing party from crossing over and supporting a candidate they sincerely wanted to support.  Another problem is that there are scheming people (we all know we are out there for sale to the highest bidder) who will change their party affiliation well  in advance, just to be "sleepers" for the eventual goal of jamming a candidate their original party fears.  I don't see an easy solution here to the crossover, except to find an extraordinary candidate who is willing to put up with the horros of political smear in order to attainthe higher good. There aren't many of them out there., Hope we have one this year who will continue to take the high road away from the mud.