Events at the turn of the century closed out this second era of executive-legislative relations. The political realignment generated by William McKinley's triumph in 1896 paved the way for closer partisan coordination between the executive and legislative branches (most prominently during Woodrow Wilson's presidency). As in the early years of the republic, party unity tended to dilute the strength of institutional conflicts and give the president more leeway. McKinley also employed a more active foreign policy, with the United States intervening in the Cuban-Spanish colonial war and then occupying the Philippines. The congressional response to the two conflicts provided a good demonstration of the range and limitations of the legislative role in turn-of-the-century international affairs. Regarding Cuba, consistent congressional pressure factored into McKinley's decision to declare war; at the same time, however, the Teller Amendment, which committed the United States to supporting Cuban independence, limited the president's options in 1899 and 1900. Consideration of the Treaty of Paris, under which the United States annexed the Philippines, offered a similarly ambivalent legacy. The Senate featured some of the imperialism debate's most articulate intellectual offerings. George Hoar was among the nation's most out-spoken anti-imperialists, while Albert Beveridge countered that annexation would allow the United States to enter the ranks of the world's great powers. But the ultimate approval of the treaty had less to do with rhetoric than with congressional logrolling: McKinley granted Louisiana's Democratic senators control over the state's federal patronage in exchange for their votes, which allowed the administration to reach the two-thirds total required.
In addition to the political realignment, other domestic factors influenced the congressional role in early 1900s foreign policy. Political activists in the Progressive Era, convinced of the inherently corrupt and conservative nature of Congress, championed a strong presidency as a base for reform. Meanwhile, the intellectual currents of the time envisioned the United States assuming a more active, even moralizing, international presence, a mindset that guided not only McKinley's Cuban and Filipino policies but much of his successor's agenda as well. These changes shattered the nineteenth-century balance of power between the two branches. Instead, the executive undertook frequently unsanctioned, aggressive moves, as in Theodore Roosevelt's sending troops to assist the 1903 Panamanian revolution or his establishing a U.S.-sponsored customs receivership in the Dominican Republic in 1905. Use of unilateral executive actions climaxed during the Wilson presidency, during which U.S. forces were dispatched to Mexico, Russia, Haiti, and the Dominican Republic.
Although the Gilded Age system thus came to an end, Congress certainly remained a restraining influence on Progressive Era presidents. The one clear executive victory on a treaty during this period—the approval of the Treaty of Paris—occurred only because of McKinley's skillful management of Congress during both the negotiating and approval processes. McKinley's successors lacked either his political tact or luck and paid the price. In 1905, for example, Theodore Roosevelt explained that he had not submitted a treaty to implement the Dominican customs receivership lest the future Foreign Relations Committee chair Augustus Bacon, "backed by the average yahoo among the Democratic senators," block the measure to get "a little cheap reputation among ignorant people." During the presidency of William Howard Taft, the Senate not only refused to approve proposed arbitration treaties with Britain and France but also denied attempts to create protectorates over Honduras and Nicaragua. While the Senate's rejection of the Treaty of Versailles ending World War I might have served as the highest-profile example of congressional power during the Progressive Era, it was not an isolated example of the upper chamber asserting itself on international matters.