The power of incumbency does not come from citizens believing their rep does a great job, it comes from money putting that rep in the public eye. People in general will vote for who is put in front of their face the most. "I've heard of this guy, never heard of that other guy so much, so this guy it is. Now home to the TV."
If people couldn't vote for lower offices simply because they showed up for presidential votes, but rather had to show up to vote on another date for other elections, then only people who actually cared about lower offices would vote for those. I think that might make it a lot harder to keep incumbents in power.
Local elections, whenever they're held, are a real problem; unless I have real knowledge about a candidate I don't vote. My parents and I all pool our information together (e.g. my father knows which county commissioner is an idiot, and I, oh, research judges) and even then there are a lot of offices we don't vote on. And some run unopposed, e.g. our county clerk is very competent.
But that doesn't mean this is all a generally useless exercise, if an abusive public administrator, or a sheriff who doesn't play well with others is up for reelection, at least where I live they will be sent back home to spend more time with their families, or eventually to Federal prison in the case of the administrator.
A great quantitative example of this is in the (somewhat dry) "Rise and Fall of the American Whig Party" by Michael Holt. While it talks about a very different time, the demonstration that the party that got the most of its voters to vote always won was pretty convincing.
And you don't even have to win -- just force her to stop being complacent and change her outrageous positions in order to mitigate the risk of losing.
Not if they win.
And I don't see why you need a party insider in any event. What you need is someone who can fund their own primary campaign, or who can get enough donations from real people to do it, i.e. someone who is famous or rich or both.
>Schwarznegger could possibly have beaten her, but a) he had a sleazy sex scandal and b) CA Republicans seem to dislike him even more than democrats because he has the temerity to take things like global warming seriously.
Schwarzenneger could possibly have beaten her because he's rich and famous, but he's not the only one with those characteristics.
Ditto Barbara Boxer.