Democrats in the Suffolk and Middlesex District must make a choice Sept. 1 they have not had to make in more than a decade: who to seat in the state Senate.

Boston mayor Michelle Wu has endorsed her former senior aide, Daniel Lander, in his campaign against Will Brownsberger for the Suffolk and Middlesex state Senate seat.

Massachusetts senator Elizabeth Warren endorsed Daniel Lander in the Suffolk and Middlesex District state Senate race, choosing a young first-time candidate over 14-year incumbent Will Brownsberger.

The incumbent says his reelection is for “the sake of this district”; the challenger decries a system and calls him “the architect of that broken status quo.”