I don't get why those traitors (and the ones in Washington for that matter) haven't been primaried. While Republicans won a 25-24 majority in the Senate in 2014, before that, Democrats had a 25-24 majority, but two traitors caucused with the Republicans, giving them a 26-23 coalition.
Well, in Washington, it's almost definitely because of our top-two primary system. Against an incumbent Democrat with bipartisan appeal (in an open primary) and a Republican, it's hard for a "true" progressive to break into the top two and make it to the November ballot.
I agree that the top two primary may be a factor, but not so much for the reason you mentioned.
1/3 of the vote + 1 vote (or technically, 1/3 of the vote + at least 1/3 of a vote, in the same way that "50% plus 1" is really 50% plus (at least) 1/2) guarantees a candidate will make the top two in a top two primary. If a loyal Democrat running against a Democrat caucusing with the Republicans and a Republican can't get 1/3 of the vote, even with turnout likely being lower and a bit more conservative, I doubt that person would be able to knock off an incumbent with bipartisan appeal if the Republican candidate was eliminated instead.
Such a candidate could perhaps win a traditional primary, but a more likely way I think the top-two primary could help an incumbent who is a member of one party but is willing to make deals with the other is if the other party doesn't get a candidate in the top two so all their voters will support the wheeling-dealing incumbent rather than the party loyalist challenger whose positions are even further from there's. Those voters plus enough independent and "soft" voters for the incumbent's party might often be enough for the incumbent to win.
I don't follow Washington State politics very much though, so I might be totally wrong, but theoretically a "trans-caucusing" incumbent who wins reelection due to the top-two method should more likely win because they get most votes from the party they caucus in "runoff" (not really a runoff I know), not because the loyalist challenger who would win in a normal primary fails to make the top two.
Similarly to how Joe Lieberman won the general against Ned Lamont in 2006?
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