Only 24% of registered voters in California are Republican, so the election hinges on the Democratic primary. You don't get to a position in a political party w

Only 24% of registered voters in California are Republican, so the election hinges on the Democratic primary. You don't get to a position in a political party where you can realistically run for and potentially win a US Senate seat by making a habit of attacking people in your own party. Those that do get ostracized long before they have that kind of juice, and the people who could potentially do it are not likely to risk the entire thing on running now when they could more safely run in another term or two, especially if they've already got a comfortable elected position. So the answer on the inside is that nobody willing to run against her has the power to, and nobody with the power to is willing. On the outside, it's people who don't care who is running, they only care about the letter next to the name, so would never vote for a Republican or an Independent.