William "Mo" Cowan, a Boston-based attorney and former top aide to Massachusetts Gov. Deval Patrick, was sworn in as an interim U.S. senator on Wednesday. He is filling the seat held for decades by John Kerry, who last week was confirmed as the new secretary of state.

Vice President Joe Biden administered the oath of office to Cowan. In a tender moment during a re-enactment of the swearing-in in the Old Senate Chamber, the vice president held the face of Cowan's son Miles, 8, recalling for the awestruck boy how his own sons were about the same age when he was first sworn in as a senator.

In addition to Cowan's family, Patrick, Kerry and Massachusetts Sen. Elizabeth Warren attended the ceremony and extended their support during his time in Washington.

Cowan, who will not compete for the job in June, is the state's second African-American senator. The first was Republican Edward M. Brooke.

He told reporters that he felt like a kid who has joined a new school mid-semester, but it is "definitely a thrill" to be a part of the Senate. Cowan also said he is very pleased that the first vote he will cast is for a significant piece of legislation, the Violence Against Women Act.
Cowan said that he looks forward to focusing "on the things that matter most to the people of Massachusetts — jobs, the economy, affordable health care and making sure we continue to fund and invest in education."

For the first time in history, two African-Americans will serve in Congress' upper chamber. South Carolina Sen. Tim Scott warmly greeted Cowan on the Senate floor with a handshake and a hug.

"He welcomed me to the Senate as a new colleague and remarked that he's only been here a few weeks himself, so he's still learning his way around, but he offered his support and assistance," Cowan said. "I said I'd love to sit with him and learn a little bit more about him and he about me and see if there are ways in which we can work together."

Cowan added that he plans to work closely with colleagues in the Democratic caucus and across the aisle.

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  (Photo: Alex Wong/Getty Images)