Sen. Dianne Feinstein (D-CA), who's worked in the senate since 1992, announced on Twitter and Facebook today that she will run for reelection next year, claiming there's "Lots more to do" and that she's "all in!"

Why this matters: At 84, Feinstein will be running for her fifth full term, and despite speculation she might have trouble facing off other Democratic candidates, no prominent opponent has yet to emerge.