Senator Edward Markey, who began his congressional career in 1976, faces a challenge from Representative Seth Moulton.

© Mel Musto for The New York Times; Josh Reynolds/Associated Press

A judge temporarily blocked the agency from implementing a strict new rule governing mail voting. The policy could disproportionately affect Democrats and many battleground elections.

© William Liang/Associated Press

Senator Ed Markey of Massachusetts has emerged as a vocal defender of transgender rights as he tries to fend off a primary challenge from Representative Seth Moulton.

© Mel Musto for The New York Times