Which Senators will retire in 2016?

[Attorney General & PPT Dwarven Dragon]

Short Version: I expect McCain, Grassley, Paul, Wyden, Boxer, Mikulski, Vitter, Crapo, Schumer, and Rubio to retire. The first four would make previously uncompetitive races competitive, while the rest would keep the race at essentially the same level of competitiveness.

Long Version:
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A * indicates that I expect the senator to actually retire.

If any of the following run again, they'd be safe or very close to it, but these races would become more competitive in the event of a retirement:
McCain (R-AZ) *
Grassley (R-IA) *
Paul (R-KY) *
Isakson (R-GA)
Boozman (R-AR)
Wyden (D-OR) *
Blumenthal (D-CT)

These Senators' retirements would have essentially no effect on the competitiveness of their races (# indicates competitive race):
Boxer (D-CA) *
Mikulski (D-MD) *
Murray (D-WA) #
Bennet (D-CO) #
Hoeven (R-ND)
Thune (R-SD)
Vitter (R-LA) *
Moran (R-KS)
Lee (R-UT)
Crapo (R-ID) *
Lankford (R-OK) (Safe R race in Nov. 2014)
Scott (R-SC) (Safe R race in Nov. 2014)
Schatz (D-HI) (Safe D race in Nov. 2014)
Shelby (R-AL)
Coats (R-IN)
Burr (R-NC) #
Leahy (D-VT)
Schumer (D-NY) *
Murkowski (R-AK)
Toomey (R-PA) #
Rubio (R-FL) #*
Blunt (R-MO) #

In these already competitive races, a retirement would help the democrats:
Kirk (R-IL)
Reid (D-NV)
Ayotte (R-NH)
Portman (R-OH)

In this already competitive race, a retirement would help the republicans:
Johnson (R-WI)