Chris Van Hollen was sworn in as Maryland's new U.S. senator Tuesday.
The Democrat told News4 he is already preparing to grill President-elect Donald Trump's cabinet nominees.
"I have great trouble with some of his nominees, but I'm going to listen to their testimonies," he said.
Vice President Joe Biden, who conducted the official swearing in, thanked Van Hollen for his help playing Republican Sen. Paul Ryan during Biden's preparation for the 2012 vice presidential debate.
Van Hollen, who served seven terms in the House, won the seat that opened with the departure of Barbara Mikulski, who retired after serving 30 years in the Senate.
Maryland also had two new House members sworn in Tuesday: Democrats Anthony Brown and Jamie Raskin.
Brown is a former lieutenant governor during then-Gov. Martin O'Malley's administration from 2007 to 2015 who ran for governor two years ago but lost to Republican Gov. Larry Hogan. He represents Maryland's 4th Congressional District.
Raskin is a former state senator from Montgomery County. Raskin represents Maryland's 8th Congressional District.