[Guest post by Noam Scheiber:]

Per this excellent Times story, it appears that Palin's opposition to just-defeated Alaska Senator Lisa Murkowski stems not from ideological differences or even tactical disagreements but ... a personal slight:

Many people expected Ms. Palin to run against Ms. Murkowski herself once 2010 arrived, but Ms. Palin made a point of saying she would not. Fresh off the newfound fame created by the 2008 presidential campaign, she created a political action committee and made a show of donating to Ms. Murkowski’s campaign in early 2009.
A few months later, Ms. Palin stunned the state by resigning. Ms. Murkowski, rarely confrontational, passed succinct judgment.
“I am deeply disappointed that the governor has decided to abandon the state and her constituents before her term has concluded,” she said.
By the following spring, Ms. Palin was backing Mr. Miller [in the GOP Senate primary for Murkowski's seat], an ally for several years, and she had reframed her initial support for Ms. Murkowski.
“With no one willing to challenge the political machine at the time, and amid rumors that I would challenge Lisa Murkowski for the U.S. Senate, SarahPAC contributed to Lisa’s campaign,” Ms. Palin wrote on Facebook in June. “As she and I discussed, this was an attempt to reassure the senator that I, as Alaska’s governor, had no intention of jumping into the race.”

As it happens, this change of heart fits a pattern that pretty much explains Palin's entire political career. If you dig hard enough, you almost always find some perceived slight--usually at the hands of some member of the establishment (or what passes for the establishment in Palin's mind)--behind every decision Palin has made to run for office or oppose another politician. There really isn't much more to it than that.