His decision likely sets up a rematch with Sen. Ron Johnson in 2016.
Rep. Adam Schiff is not running for retiring Sen. Barbara Boxer's seat.
Eight of 10 hotly contested races are for seats held by Republicans.
Rep. Ron DeSantis's (R-Fla.) bill would not apply to current lawmakers.
Sen. Kelly Ayotte (R) leads Gov. Maggie Hassan (D) by 5 percentage points.
Jonathan Easley 05/06/15 10:11 AM EDT
The conservative favorite is a 36-year-old Iraq War veteran.
McCain's approval rating is under water.
The DSCC is targeting nine GOP senators for past opposition.
Rebecca Shabad 04/29/15 11:16 AM EDT
Democrats say the incident has thrust Rep. Elijah Cummings into a leadership role.