It was pretty much inevitable, although recently there were noises he was going to run for re-election (the Republican field is pretty big, and fragmented, at the moment), and so one was left sitting on the edge of one's chair.
The senior U.S. Senator from Nebraska is 70 years old, and unlike other states, seventy is "old" for a politician; we tend to encourage them to retire out to pasture before then.
He would have faced a tough re-election, given his caving in on the 0bama health care debacle; but again, the splitting of the Republican votes for various candidates in the primary perhaps gave him some hope.
We're probably going to see two things happen now: one is that Scott Kleeb, a failed candidate for the U.S. House in 2008 and a failed candidate for the U.S. Senate in 2010, is going to be touted again as the Democrats' best hope for holding onto this seat. He's reasonably young, he's charismatic, and superficially "conservative."
I guess the best way to counter that is by reminding Nebraskans the old adage: if one's conservative, better to support a "liberal" Republican than a "conservative" Democrat. When push comes to shove, a liberal Republican will vote with the majority of his party, which is conservative, while a conservative Democrat will vote with the majority of his party, which is liberal.
We can afford to give liberal Republicans a few crumbs now and then, since they help us getting a bigger piece of the loaf.
However, probably much to the relief of the "100%"ers here, all the Republicans running for the seat are safely and strongly conservative anyway, so that issue's irrelevant.
The other thing that's probably going to happen is that Nebraska Republicans will start coalescing behind one candidate, instead of as we are, being split among about six.
My personal preference is for Deborah Fisher, a rancher-attorney from dutch508's part of Nebraska, the western edge of the Sandhills--she would certainly cancel out the probable Democrat candidate's "cowboy" allure--but I'll be happy with whoever the (R) candidate is.