That said, the League of Nations fight represented the most significant foreign policy confrontation between Congress and the executive in the first half of the twentieth century. It is ironic that failure to obtain Senate approval of the Treaty of Versailles plays such a role in Woodrow Wilson's historical legacy, because, in his first six years in office, Wilson had compiled a record at managing Congress unmatched by any chief executive since Thomas Jefferson. Using adept political skills, effective management of the Democratic caucus, and a keen ability to articulate his political vision to the public, Wilson had managed to push through Congress not one but two comprehensive reform packages. His record on foreign policy matters was slightly less stellar, but, nonetheless, given the complexity of the issues he confronted—not only the Great War but also the Mexican Revolution—he performed impressively.
By handing control of Congress to the Republicans, however, the 1918 midterm elections elevated Massachusetts senator Henry Cabot Lodge to the dual position of Senate majority leader and chair of the Senate Foreign Relations Committee. Personal and partisan animus shaded Lodge's response to Wilson. Before Wilson's arrival on the national scene, Lodge (who, like Wilson, held a Ph.D. degree) had been the nation's most prominent scholar in politics. Lodge, who matched Wilson's partisanship, also recognized that the treaty's unamended passage would benefit the Democrats politically. The senator confronted a problem, however: the League of Nations seemed popular, and opinion among his Republican colleagues was badly divided. A few Republican senators, such as William Borah and Robert La Follette, opposed entering the league under any circumstances, primarily because they believed that European imperialist powers would dominate the organization. "Mild reservationists," such as senators William Kenyon and Porter McCumber, supported the treaty with only minor changes. Most Republicans joined Lodge in classifying themselves as "strong reservationists," a vague designation that amounted to outright opposition to the league as constructed by Wilson.
The treaty reached the Senate in the spring of 1919. Lodge's performance between then and the first vote on the document in November 1919 provided a textbook example of how a congressional minority could use the institution's powers to alter U.S. foreign policy. Lodge began by convening lengthy hearings on the treaty, which gave the Republicans time to influence public opinion. But the hearings also exposed the many provisions in the Versailles Treaty in which diplomatic necessities had forced Wilson to compromise his ideals. As the summer progressed, criticism of the treaty escalated, from a wide variety of groups—ethnic Americans, especially of Irish ancestry, who saw the document as a sellout to the British; radicals and anti-imperialists, who viewed the treaty as a betrayal of American ideals; and nationalists, who worried that the collective security mechanism of Article X would rob Congress of its constitutional right to declare war. As a Senate critic, Lodge did not need to propose a positive alternative; he only had to ensure that one-third plus one of the members of the Senate would vote against approval. His determination, along with Wilson's equally passionate refusal to compromise and the parliamentary tactics of the Senate irreconcilables (the outright opponents of the league), paved the way for three Senate votes in which the upper chamber rejected the Treaty of Versailles and thus U.S. membership in the League of Nations.
The defeat of the Versailles Treaty confirmed the breakdown between Woodrow Wilson and the new Republican majority. But even before the 1918 elections, relations between the two branches had deteriorated. Before the U.S. entrance into World War I, the president was subjected to consistent barbs from Senate progressives for both his Mexican and his preparedness policies. Then, in 1918, Wilson confronted the dilemma of Congress exercising a prior restraint over his response to the Bolshevik Revolution: fear of a congressional investigation blocked a scheme to supply credits to Admiral Aleksandr Vasiliyevich Kolchak's antirevolutionary forces. When Wilson attempted to bypass Congress entirely by sending troops to Russia, the body employed the ultimate sanction: its power of the purse. In 1919 a resolution introduced by Senator Hiram Johnson to cut off funding for the intervention failed on a perilously close tie vote. This demonstration of the critical spirit in Congress convinced the administration that it had no choice but to withdraw the armed forces.
The intensity of the Versailles and Russian battles heightened the importance of foreign policy pressure groups of all ideological persuasions. The pattern continued during the 1920s, especially on military and Latin American issues. As would be the case later in the century as well, such groups tended to influence Congress more than the executive. In 1926, for instance, the U.S. Army's Chemical Warfare Service waged a highly effective lobbying campaign to prevent Senate approval of the Chemical Weapons Treaty, while anti-imperialists and peace groups helped soothe the U.S.–Mexican crisis of 1926–1927. In turn, the greater public interest in foreign policy highlighted the ability of Congress, especially the Senate, to frame consideration of international questions, especially at a time when political reporters spent as much time covering events in the Senate as they did at the White House.
No figure made better use of this environment than William Borah. Combining his power as Foreign Relations Committee chair with his long-standing identification with the issue, Borah positioned himself as the chief interpreter of the 1929 Kellogg-Briand Pact to outlaw war. He also launched his own venture in private diplomacy in an attempt to prevent a military conflict with Mexico. Those executive initiatives that cleared Congress during the 1920s, such as the Washington Naval Conference treaties of 1921–1922, further confirmed the legislature's influence: the treaties overcame strong Senate opposition largely because the Harding administration appointed two prominent senators, Henry Cabot Lodge and Oscar Underwood to the U.S. negotiating team. When Secretary of State Frank Kellogg proved less willing to involve Congress in his Latin American policy—during his tenure the United States sent marines to Nicaragua without congressional sanction and nearly severed diplomatic relations with Mexico—the legislature responded in kind: in 1929 the Senate passed an amendment authored by C. C. Dill to terminate appropriations for the U.S. intervention in Nicaragua.
The Dill Amendment was the handiwork of the peace progressives, one of the most effective congressional blocs of the twentieth century. Although never more than twelve in the Senate, members of the group displayed remarkable acumen in advancing their ideological agenda. They first attracted notice in the 1910s, when senators such as Borah, La Follette, and George Norris offered an anti-imperialist, antimilitarist critique of Wilson's foreign policy. But the peace progressives made their mark in the 1920s, when they used the Senate's traditional tolerance of dissenters to influence the foreign policy of the Harding, Coolidge, and Hoover administrations. Their tactics included appropriations riders, public hearings to influence popular opinion, covert cooperation with peace groups to leak embarrassing information, and using the prestige of their positions to cement transnational alliances with like-minded groups and individuals overseas. By the end of the 1920s, U.S. policy toward Central America and the Caribbean had moved strongly in an anti-imperialist direction.
And so, as the framers anticipated, foreign policy issues remained vigorously contested between the branches. This framework continued during the first several years of Franklin Roosevelt's administration. A domestic focus made Roosevelt reluctant to spend political capital on international matters, such as the protocol for adherence to the World Court—one reason why the Senate defeated the treaty. A leading opponent of the World Court was the peace progressive senator Gerald Nye, who, like many in the group, believed that pressure from munitions makers and bankers explained Wilson's decision to bring the country into World War I. In the throes of the Great Depression, a conspiracy theory against business carried a good deal of weight, and, when Nye opened hearings on the matter in 1934–1935, the affair attracted national attention. Secretary of State Cordell Hull complained how the Nye Committee's dominance of discourse on neutrality issues strengthened isolationist sentiments. Indeed, as the secretary anticipated, the hearings resulted in Congress passing the Neutrality Acts of 1935 and 1936. Ironically, during Franklin Roosevelt's first six years as president, the most important diminution of congressional authority on foreign policy issues came with the Reciprocal Trade Agreements Act of 1934, when Congress willingly surrendered its power over foreign economic policy as part of the fallout from the Smoot-Hawley tariff.
Despite differences between eras, some common patterns emerged in the congressional approach to international relations between 1789 and 1941. The Dill and Hiram Johnson resolutions, for example, showed how powerfully military appropriations bills could influence foreign affairs. The prevalence of treaties, even though the upper chamber approved 86 percent of the 726 treaties it considered between 1789 and 1926, heightened the importance of formal roll-call votes in assuring at least some senatorial presence in the conduct of foreign policy. With the (albeit important) exception of tariffs, the House of Representatives played a minor role on international questions. (During one congressional session in the 1920s, for instance, the House Foreign Affairs Committee spent a week debating a $20,000 appropriation for an international poultry show in Tulsa, which one member recalled as the committee's most important issue of the whole session.) In the Senate, meanwhile, the Foreign Relations Committee reigned supreme. The upper chamber's considerable international powers fell under the control of a relatively small foreign policy elite, composed of Foreign Relations members and the few other senators—like the peace progressives—who exhibited intense interest in international matters.
The international threat associated with World War II altered this alignment. Perhaps no single piece of legislation highlighted the change more than the Lend-Lease Act of 1940, which passed despite knowledge that it would lessen congressional control over foreign policy. During World War II, determined to avoid the mistakes of the Wilson administration, Roosevelt hoped to place the Senate on record supporting U.S. participation in a postwar international organization. But the president did not want Congress to play an active role in forming postwar foreign policy. He strongly opposed the so-called B2H2 resolution (abbreviated for its sponsors—Senators Harold Burton, Joseph Ball, Lister Hill, and Carl Hatch), which called for the United States to join a postwar international police force. Working with Senate leaders, the administration instead championed a vaguely worded offering that praised the work of Cordell Hull at the 1943 Moscow Conference of foreign ministers. This was the first in a series of measures in which Congress was asked to provide advance authority for future executive action. Moreover, as would occur with similar postwar resolutions, the political and international conditions under which the Senate considered the substitute—after Hull had already completed his work—made it almost impossible to oppose the bill without repudiating executive commitments.