Republicans show up disproportionately in California primaries. This has occurred when there were big Republican primary battles on the ballot and when they're weren't. It's occurred in Republican years and Democratic years. Statewide the registration is 43%D/30%R/27%other. This year ballots have been returned via mail at 44%D/38%R/18%other. The low turn-out from independents and minor parties is normal. They often don't have anything to vote for in June as they've been excluded from party primaries. The high Republican turn-out fits with the past. In CA-30 the turn-out so far is 52%D/33%R/15%other. This is 4 points above the district's Democratic registration, but 7 points above Republican registration.
This poll has the vote going 57.5%D/16%R/3.5G. The remaining 23% are undecided. The Democratic number looks fairly close, but the Republican number is way off.
Either one of three things is happening:
1. The pollster is using a sample that's around 65D/20R/15I
2. Most of the undecideds are usually Republican voters.
3. Republicans are voting for Democrats.
I suspect that it's mostly the 1st, a bit of the second and third. It makes sense for Republicans to be more undecided since their candidates are largely unknown. It doesn't make sense for almost all the undecideds being Republicans, especially since they are turning in ballots at a good rate. Some Republicans will vote Democratic. I think that's between 10% and 25%. No more. We're in a state where people are leaving the Republican Party. If you're staying in, there's nothing anyone can do to convince most Republicans to vote for a Democrat. It's my suspicion that pollsters think this is a Democratic district. Thus, most of the votes will be from Democrats.
Maybe I'm wrong. We'll see Tuesday.