Massachusetts Democrats will decide the latest head-to-head matchup between the party's moderate and progressive wings. This time, top progressives are backing the incumbent.

In Massachusetts, the octogenarian senator Ed Markey faces a challenge from a much younger centrist, Representative Seth Moulton.

© Mel Musto for The New York Times

The 2026 midterms have brought a number of generational challenges like the one Moulton is waging against Markey, with younger Democrats taking on — and in some cases unseating — longtime incumbents.