1938 Midterm Elections
Republicans had lost seats in both houses of Congress in 1930, 1932, 1934, and 1936. Their totals were a mere 88 seats in the House and 16 seats in the Senate. Following President Franklin D. Roosevelt's landslide reelection in 1936, he attempted to pack the Supreme Court with six new justices to neutralize conservative Justices who struck down some of his New Deal programs as unconstitutional. It received backlash from his own party as an overreach of executive power.
Roosevelt's political standing was also damaged by a sharp economic downturn in 1937 and 1938. Unemployment rose from 5 million Americans to more than 12 million, manufacturing, consumer spending, and personal income all declined. Critics dubbed it the "Roosevelt Recession" and seemed to vindicate Republican attacks on the New Deal. According to an August 1938 Gallup poll, 66% of Americans wanted FDR to take more conservative policies. 
During the election, Roosevelt launched a campaign to "purge" conservative Democrats in primaries. With a few exceptions, almost all of his endorsed candidates lost. Republicans made significant gains, and won the governorships of Pennsylvania, Ohio, and Michigan. Although Democrats retained a clear majority in the House and Senate, most of the incumbent Democrats that were defeated were pro-New Deal Democrats. Conservatives were now the majority in Congress and Republicans were large enough to be an effective opposition. One notable freshman was future Senate Majority Leader Robert Taft of Ohio.