 He was elected as an at-large member in 1941, and served until resigning in 1942.In 1942, Mruk was elected to the U.S. House as a Republican, and served one term (1943-1945) as the representative of New York's 41st District.In Congress, Mruk questioned the Soviet Union's intentions for post-World War II Poland; as the Soviets were still part of the Allied effort against Nazi Germany, Mruk's concerns prompted assurances from President Franklin D. Roosevelt that Poland would not lose its sovereignty.