Senator Kay Bailey Hutchison, Republican of Texas, who is a candidate in her party's 2010 gubernatorial primary, will stay in the Senate, at least until after that March primary.
Hutchison had planned an earlier resignation from the Senate, perhaps as early as this fall. But with the two parties' numbers in the Senate being so close to the dividing line between filibuster and cloture, she doesn't want to make that move just yet.
Of course, one implication of that schedule is that, if she loses the primary, she can hold on to her Senate seat, and seek reelection in 2012. Polls show her trailing her primary opponent, incumbent Governor Rick Perry, by a significant margin.
If Hutchison makes a comeback and defeats Perry, the timing of a special election for her Senate seat would depend on the timing of her resignation. As Josh Kraushaar explains in Politico, that could mean either a May or November special election.