Cowan, flanked by Sen. Elizabeth WarrenElizabeth WarrenFranken emerges as liberal force in hearings Women's marches draw huge crowds as Trump takes office Warren: 'I'm here to fight back' MORE (D-Mass.) Kerry, was sworn in by Vice President Biden. He is now the Senate's second black senator, and the only black Democratic senator.

He will serve until a special election to replace Kerry occurs in June. Democrats are likely to retain the seat, as Massachusetts Republicans have been unable to front a strong challenger since former Sen. Scott Brown (R-Mass.) decided against a run.

Reps. Edward MarkeyEd MarkeyBuying that new-used car: Congress must put safety first Overnight Finance: Scoop – Trump team eyes dramatic spending cuts | Treasury pick survives stormy hearing Senate Dems want Trump to withdraw from Pacific trade deal MORE and Stephen Lynch have both announced their intentions to pursue the Democratic nomination for the seat, and face a primary on April 30.