Arizona Senator Jon Kyl announced today that he will not run for reelection in 2012--that makes him the fifth senator to do this in about a month, for those who are counting. First, on Kyl: The minority whip was elected in 1994, and since then has fought aggressively for the conservative cause. Both a supporter and a critic of George W. Bush, Kyl is known for his staunch defense of the Iraq and Afghanistan wars as well as his successful crusade against Harriet Miers, Bush's pick for White House counsel. Kyl also spearheaded a 2005 search for wealthy business owners who died in Hurrican Katrina to make a case for repealing the estate tax (after an expected vote on the tax was held off in response to the storm).

Here's an idea why Kyl might have decided it was time to throw in the towel: though recent polls predicted Kyl had a good chance of being reelected, Republican party rules mandate that he would have had to step down from his post as whip should he hold onto his seat in 2013. Another hint that Kyl was not gearing up for another run was his modest fund raising to date compared with how much he had raised around this time during the last election.

Let's get back to these numbers, though. The Senate retirement blitz has been pretty impressive. Last month, fellow Republican Kay Bailey Hutchison of Texas made clear she would not seek reelection. In the weeks since, we've heard retirement announcements from Democrats Kent Conrad from North Dakota, Joe Lieberman of Connecticut, and, as of yesterday, Virginia's Jim Webb. The soon-to-be-open seats propose a shake-up to the Democratic majority in the Senate, so predictions for who will take over are already being made. But what we at The Wire want to know is this: why are all of these senators choosing right now to announce their retirements? Is this just a developing "all-in-or-all-out" moment in the ever-shortening campaign cycle? Or is there something in the water over there on the Hill?