His surprise announcement may mean that he expects John Hoeven to run for Senate. Here’s what I wrote about the race a few weeks ago:

NORTH DAKOTA: Right now, there’s only one poll that matters — the one in the head of Republican governor John Hoeven. If he decides to challenge Democratic senator Byron Dorgan, he becomes an instant favorite. If he declines the opportunity, Dorgan almost certainly cruises to reelection. In November, a Zogby poll gave Hoeven a commanding lead, 55 percent to 36 percent. Expect Hoeven to announce his decision around the New Year. TOSS-UP.

With Dorgan out, this may be the GOP’s best pick-up opportunity in 2010.