WASHINGTON — The usually pin-drop-quiet Senate gallery erupted in applause Thursday after William “Mo” Cowan was sworn in as the newest senator from Massachusetts.

Vice President Joe Biden administered the noontime oath to Cowan, a Democrat and former chief of staff to Massachusetts Gov. Deval Patrick. Appointed by the Democratic governor, Cowan will temporarily fill the seat opened by John Kerry’s confirmation as secretary of State. A special election will be held June 25 to permanently fill the seat.


“Congratulations, Senator. Welcome,” Biden said, as guests of the new senator, as well as visiting tourists, rose in applause.

Kerry and newly elected Massachusetts Sen. Elizabeth Warren were at Cowan’s side.


Cowan was quickly congratulated by Republican Sen. Tim Scott of South Carolina, the chamber’s only other African American senator, who was also appointed by his state’s governor after a vacancy. The two men shared a handshake, and a hug, in a rare moment in the chamber where diversity has trailed that of the nation.

Never before has the Senate had two blacks serving at the same time, according to the Senate Historical Office.


Cowan is not expected to run for the seat in the special election.

Two Democrats, Rep. Ed Markey and Rep. Stephen Lynch, have announced their intentions to run. Former Republican Sen. Scott Brown, who lost his reelection bid in 2012 to Warren, has opted not to seek the office.


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Lisa.Mascaro@latimes.com


Twitter: @LisaMascaroinDC