Former Los Angeles mayor's decision makes Kamala Harris (D) a heavy favorite for open seat.
Former California Republican Party Chairman Tom Del Becarro has formed an exploratory committee for the seat, while Republicans continue to push former Rep. David Dreier (R-Calif.) to jump into the race as well.
The former Democratic governor will reportedly challenge Sen. Rob Portman (R) in 2016.
The former Wis. senator is Democrats' best hope to challenge GOP Sen. Ron Johnson in 2016.
The DSCC brought in $4.5 million — $2 million more than the NRSC last month.
The National Republican Senatorial Committee ended last month with $4.1 million in the bank.
Democrat Jason Kander was also an Army Captain in Afghanistan.
The former governor and presidential candidate squashes speculation of a primary challenge.
Florida senator visits early-voting states to promote his new book.
The Democratic governor of New Hampshire hasn't said whether she'll run for Senate but could be a formidable challenger to Ayotte.