In November 1934, 1936, and again in 1942, Hart was defeated in the general elections by Republican Fred L. Crawford. In 1940, he was an unsuccessful candidate in the Democratic Party primary election for a United States Senate seat. Hart was a delegate to the Democratic National Conventions from Michigan in 1932 and 1944.
Hart lost his bids for re-election in 1934, 1936, and 1942 to Republican Crawford. In 1940, he didn't make it past the Democratic primary for a Senate seat. Hart represented Michigan at the Democratic National Conventions in 1932 and 1944.