In 1938, Wasielewski unseated incumbent Congressman Raymond Joseph Cannon in the Democratic primary for Wisconsin's 4th congressional district, but was narrowly defeated in turn by a former incumbent, Republican John Schafer, with 33,559 votes (31.40%), to Schafer's 34,196 (32.00%),
Wasielewski was again nominated in 1940, and this time was elected to the 77th Congress.