Senate retirements keep piling up. Jon Kyl makes it five this cycle:

Senate Minority Whip Jon Kyl will announce Thursday that he is not running for reelection in 2012. The second-ranking Republican in the Senate is expected to make the announcement at 12 p.m. ET from his home state of Arizona.

Kyl joins Hutchison (R-TX), Lieberman (I-CT), Webb (D-VA) and Conrad (D-ND) among the ranks of Senators whose terms expire at the end of 2012 but who are not seeking re-election. This is a pretty brisk pace, but isn’t record-breaking:

Excluding the appointment due to death in West Virginia, the 14 open seats in 2010 matched the modern day political record set in 1996 when 13 Senators retired and one other -- appointed Kansas Sen. Sheila Frahm (R) -- lost a primary. In the intervening six election cycles, however, the number of retirements -- forced or otherwise -- dipped considerably. In the 1998, 2000, 2006 and 2008 elections there were only five Senate retirements each. In 2002, there were seven retirements while in 2004 there were eight.

Arizona, like the NY-26, has a Cook PVI of R+6. However, that is somewhat inflated by John McCain, who overperformed there in 2008, since Arizona is his home state. The real number is probably more like R+4, which is much more doable with the right candidate.

Who might that candidate be? According to PPP, it won’t be former Governor Janet Napolitano, who now has a significantly negative favorable rating in the state. It also won’t be Representative Gabrielle Giffords, who simply is not in a position to engage a Senate campaign right now. The Dem who currently polls best in Arizona is 2010 gubernatorial nominee Terry Goddard, but this is almost certainly a case where Democrats are better off nominating someone less well-known.

Kyl’s retirement is a very big deal for Republicans, too. Since Kyl is the second ranking member of the Senate GOP, this will set off a leadership fight (paging Jim DeMint). Additionally, with three GOP House freshman in Arizona, long-time Rep. Jeff Flake eyeing a run, and former Rep. J.D. Hayworth still lurking around after his unsuccessful primary challenge to John McCain in 2010, expect a crowded, wacky Republican primary.

No matter who the candidates turn out to be, with very few good Senate pickup opportunities in 2012, Democrats need to make a strong play here.

(For more discussion on the developments in AZ-Sen, check out mille147’s diary on the rec list.)