This video frame grab image provided by C-SPAN2 shows William "Mo" Cowan, center, accompanied by Sen. Elizabeth Warren, D-Mass., left, and Secretary of State John Kerry, on Capitol Hill in Washington, Thursday, Feb. 7, 2013, to officially be sworn into the Senate by Vice President Joseph R. Biden. Cowan was chosen by Massachusetts Gov. Deval Patrick to replace Kerry. (AP Photo/C-SPAN2)

Photo by: Uncredited

This video frame grab image provided by C-SPAN2 shows William "Mo" Cowan, center, accompanied by Sen. Elizabeth Warren, D-Mass., left, and Secretary of State John Kerry, on Capitol Hill in Washington, Thursday, Feb. 7, 2013, to officially be sworn into the Senate by Vice President Joseph R. Biden. Cowan was chosen by Massachusetts Gov. Deval Patrick to replace Kerry. (AP Photo/C-SPAN2)