McSally officially running for Flake's Senate seat

Rep. Martha McSally (R-Ariz.) announced this morning that she is officially running for the Senate seat being vacated by Jeff Flake. In the primary, she'll be up against Kelli Ward, who recently attempted to distance herself from Steve Bannon. Democratic Rep. Krysten Sinema is also vying for the seat.

Why it matters: Arizona is one of two Senate seats most likely to flip Democrat, along with Dean Heller's seat in Nevada.