In 1938, after William Dieterich declined to run for re-election, Lucas was elected to the U.S. Senate over Republican
Richard J. Lyons, with a 51%–48% victory. He was re-elected
in 1944. Lucas was a
favorite son candidate and among twelve nominated at the
1944 Democratic National Convention to serve as
Franklin D. Roosevelt's running mate in the
presidential election that year. With support from
Harry S. Truman, he was elected party whip in 1946. Lucas, a moderate, drew support from both conservative and liberal wings of the party. He took over the
Midwest campaign for Truman and was credited with assisting
Truman's 1948 re-election and bringing nine Democrats into the Senate. When
Alben Barkley became vice-president and resigned his seat, Lucas became majority leader. However, he was unable to build a consensus as Senate Majority Leader with the onset of the anticommunist era, and lost in 1950, to Republican
Everett Dirksen. Lucas had become a target of Republican wrath with loss of political power in the Senate and the White House. His
1950 reelection campaign featured the active intervention into Illinois politics of Wisconsin Senator
Joseph McCarthy, who traveled the state with Dirksen saying that Senator Lucas was "soft on communism." Dirksen would go on to decisively defeat Lucas with a 54% to 46% victory. Privately, in later years, Dirksen attributed his victory to Lucas's responsibilities as Senate Majority Leader, at the apparent expense of his state; Dirksen was free to campaign locally, often debating Lucas's Illinois Democratic Party proxies and calling attention to Lucas's prolonged absence from the state. ==Policy positions==