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 first Republican to hold the seat since Reconstruction. He was reelected in 2020.
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.


== Early life and education ==
William Morgan Cassidy was born in Highland Park, Illinois, one of four sons of Elizabeth and James F. Cassidy, and is of Irish and Welsh descent. He grew up in Baton Rouge and received a Bachelor of Science from Louisiana State University in 1979 and a Doctor of Medicine from LSU School of Medicine in 1983.


== Early career ==


=== Medicine ===
Cassidy specialized in the treatment of diseases of the liver at the Earl K. Long Medical Center (LSUMC).In 1998, Cassidy helped found the Greater Baton Rouge Community Clinic to provide uninsured residents of the greater Baton Rouge area with access to free health care. The Clinic provides low-income families with free dental, medical, mental health, and vision care through a "virtual" approach that partners needy patients with doctors who provide care free of charge.Cassidy has also been involved in setting up the nonprofit Health Centers in Schools, which vaccinates children in the East Baton Rouge Parish School System against hepatitis B and flu.In the wake of Hurricane Katrina, Cassidy led a group of health care volunteers to convert an abandoned K-Mart into an emergency health care facility, providing basic health care to hurricane victims.In 2010, Cassidy's alma mater, Louisiana State University, selected him for honoris causa membership in Omicron Delta Kappa, the National Leadership Honor Society.


=== Politics ===
Cassidy was first elected to the Louisiana State Senate in 2006 as a Republican. He had previously been a Democrat, supporting Michael Dukakis for president in 1988, donating to Senator Paul Tsongas's 1992 presidential campaign, and to Louisiana Democrats Governor Kathleen Blanco in 2003 and 2004 and Senator Mary Landrieu in 2002. In 2013, Cassidy called his donation to Landrieu a "youthful indiscretion", saying that she "got elected and fell into partisan politics... Louisiana hasn't left Mary, Mary has left us." Since 2001, he has mostly contributed to Republican candidates, including Senator David Vitter. According to Cassidy, he switched parties after the extinction of conservative Democrats and because of his frustration with the bureaucracy and inefficiency of the public hospital system.On December 9, 2006, Cassidy won a special election for the District 16 seat in the Louisiana Senate. In his first bid for public office, he defeated veteran State Representative William Daniel, a fellow Republican and Libertarian candidate S.B. Zaitoon. The election was held to replace Jay Dardenne, who vacated the seat he had held since 1992 upon his election as Louisiana Secretary of State. Cassidy was sworn in on December 20, 2006. On October 20, 2007, he was reelected to a full four-year term in the Louisiana State Senate. Cassidy received 76% of the vote against Republican Troy "Rocco" Moreau (15%) and Libertarian Richard Fontanesi (9%).


== U.S. House of Representatives ==


=== Elections ===
On November 4, 2008, Cassidy was elected to serve Louisiana's 6th district in the U.S. House of Representatives, defeating incumbent Democratic Congressman Don Cazayoux with 48% of the vote. He likely owed his victory to the independent candidacy of state representative Michael L. Jackson. Jackson finished third with 36,100 votes, more than the 25,000-vote margin separating Cassidy and Cazayoux.
In the 2010 midterm elections, Cassidy easily won a second term, defeating Democrat Merritt E. McDonald of Baton Rouge with 66% of the vote. In the 2012 election, Cassidy was reelected again defeating Rufus Holt Craig, Jr., a Libertarian, and Richard Torregano, an Independent. Cassidy received 79% of the vote.


=== Tenure ===
In May 2009, Cassidy partnered with California Representative Jackie Speier to introduce legislation that would amend the House of Representatives rules to require that members of Congress list their earmark