Shipstead started as a Republican but in 1922 was elected to the US Senate under the banner of the new Farmer-Labor Party. While he generally shared the party's left-wing agenda, he rejected the extreme anti-capitalism of some members. Although he was the only Farmer-Laborite in the Senate, he won appointment to the powerful Foreign Relations Committee. Shipstead opposed U.S. entry into the League of Nations and the World Court. He called for the cancellation of German reparations, which he regarded as vindictive. Unlike non-interventionists in the Old Right, he objected to the U.S. occupation of Haiti, the Dominican Republic and Nicaragua. He blamed these interventions on the Roosevelt Corollary to the Monroe Doctrine of 1905, which had turned the United States into an arrogant "policeman of the western continent." Shipstead did not consider himself an isolationist. While he favored a policy of political non-intervention overseas, he opposed the Smoot-Hawley Tariff of 1930, which he called "one of the greatest and most vicious isolationist policies this government has ever enacted." He argued that high tariffs "raise prices to consumers" and make "monopolies richer and people poorer." Affable and dignified, his adversaries generally liked him personally. He concluded, "It doesn't necessarily follow that a radical has to be a damned fool." Along with Congressman Robert Luce of Massachusetts, he introduced the bill that enlarged the purview of the United States Commission of Fine Arts to include new buildings on private land facing federal property. The Commission, established in 1910, reviews new buildings, memorials, monuments, and public art constructed on federal property in Washington, D.C.. The bill, the Shipstead-Luce Act, is still in effect. Shipstead defected from the Farmer-Labor party in the late 1930s, charging that Communist elements were taking control. He won reelection to the Senate in 1940 as a Republican. Meanwhile, few fought more tenaciously against Franklin D. Roosevelt's efforts to enter the war in Europe. Although Shipstead voted for the declaration of war after the attack on Pearl Harbor, he still maintained his independence from Roosevelt. In October 1942, for example, he was one of the very few to vote against Selective Service, just as he had in 1940. In April 1943Isaiah Berlin, a top British expert on American politics, secretly prepared an analysis for the British Foreign Office that stated that Shipstead was: Shipstead's vote against US entry into the United Nations was entirely predictable by anyone who had followed his career. It was the capstone of decades of opposition to foreign entanglements. Like many modern conservative critics of the UN, he feared that it would foster a world superstate. But he also believed that the major powers would use the UN as a tool to dominate smaller countries. He and William Langer were the only two senators to vote against the United Nations Charter. That vote may have cost him reelection a year later. A new breed of "internationalists", led by Governor Edward John Thye and former Governor Stassen, assumed leadership of the Minnesota state GOP. In 1946, Shipstead lost the Republican primary to Thye. He retired to rural western Minnesota, where he died in 1960.
