William Morgan Cassidy (born September 28, 1957) is an American physician and politician serving as the senior United States senator from Louisiana, a seat he has held since 2015. A member of the Republican Party, he served in the Louisiana State Senate from 2006 to 2009 and in the U.S. House of Representatives from 2009 to 2015. Born in Highland Park, Illinois, Cassidy is a graduate of Louisiana State University (LSU) and LSU School of Medicine. A gastroenterologist, he was elected to the Louisiana State Senate from the 16th district which included parts of Baton Rouge, in 2006. In 2008, he was elected as the U.S. representative for Louisiana's 6th congressional district, defeating Democratic incumbent Don Cazayoux. In 2014, Cassidy defeated Democratic incumbent Mary Landrieu to represent Louisiana in the U.S. Senate, becoming the second Republican to hold the seat since the end of Reconstruction. He was reelected in 2020. He played a major role in the creation of the No Surprises Act of 2020, which instituted comprehensive balance billing protections for patients during emergency situations. Cassidy was one of seven Republican senators to vote to convict Donald Trump of incitement of insurrection in his second impeachment trial. As a result, the Republican Party of Louisiana censured him.