Manchin has called himself a "moderate conservative Democrat" and is often cited as the most conservative Democrat in the Senate. West Virginia has become one of the most heavily Republican states in the country, but Manchin has continued to see electoral success. He won the 2004 gubernatorial election by a large margin and was reelected by an even larger margin in 2008; in both years, Republican presidential candidates won West Virginia. Manchin won the 2010 special election to fill the Senate seat vacated by incumbent Democrat Robert Byrd's death with 54% of the vote. He was elected to a full term in 2012 with 61% of the vote and reelected in 2018 with just under 50% of the vote, as the state had become increasingly partisan. He became the state's senior U.S. Senator when Jay Rockefeller retired in 2015.