I think Trende’s analysis here is the best I’ve seen of this ongoing primary election cycle. These three paragraphs especially pinpoint why things are happening as they are:
We are in a deeply anti-Washington environment, both throughout the country and in the Republican Party in particular. In this environment, representatives who pay insufficient attention to what is going on in their districts are in grave danger of losing. There are two components to this explanation.
First, analysts need to understand that the Republican base is furious with the Republican establishment, especially over the Bush years. From the point of view of conservatives I’ve spoken with, the early- to mid-2000s look like this: Voters gave Republicans control of Congress and the presidency for the longest stretch since the 1920s.
And what do Republicans have to show for it? Temporary tax cuts, No Child Left Behind, the Medicare prescription drug benefit, a new Cabinet department, increased federal spending, TARP, and repeated attempts at immigration reform. Basically, despite a historic opportunity to shrink government, almost everything that the GOP establishment achieved during that time moved the needle leftward on domestic policy. Probably the only unambiguous win for conservatives were the Roberts and Alito appointments to the Supreme Court; the former is viewed with suspicion today while the latter only came about after the base revolted against Harriet Miers.
His second component notes that the politicians who understand this environment win, while those who do not lose. Read the whole thing. It will help clarify not only what has happened but what will happen in the coming months.