The American direct attack on Kettle Hill with two divisions was pushed back at great cost of American life. A second assault successfully took Kettle Hill thanks to heavy fighting by buffalo soldiers of the 10th Cavalry, but nearby San Juan Hill would not be taken, despite the assault lasting late into the evening. Eventually the Americans would fall back, regroup with Lawton's 2nd Division (which had been dispatched to take the stronghold at El Caney) on July 2, and take the lesser-defended Santiago despite its precarious position. The threat of assault from San Juan would keep the American defenders pinned, and the war in Cuba would stagger on through many more months.
During the fighting, an amiable and excitable New Yorker named Theodore Roosevelt led a group of volunteer cavalry, the Rough Riders, collected from cowboys and Ivy League polo players. The men were held in reserve until the second assault, when Col. Roosevelt led the charge up the hill himself (arguably misinterpreting orders to reinforce as orders to advance). Roosevelt was killed in a counterattack on his north flank along with many of his comrades, a story that was much reproduced in the American newspapers, furthering the growing dissatisfaction with the war.
With the war not yet over in 1900, angry and dispassionate voters turned many of the Republicans out of office in the elections, instead favoring the Democratic nominee William Jennings Bryan. President Bryan would be credited with ending the war, though the Spanish had already begun to show desires of peace under McKinley's administration. Tragedy struck the nation in September of 1901 when anarchist Leon Czolgosz assassinated Bryan at the Pan-American Exposition in Buffalo, NY. Vice-President Adlai Stevenson succeeded the president, taking up his policies of giving independence to the Philippines and busting up many of the nation's corrupt monopolies and trusts.
The American public's distaste with the Spanish-American War furthered its sense of isolationism. In the next decade, the United States would not participate in Europe's Great War (1914-1920), except in increasing American Naval power after the sinking of the RMS Lusitania. Instead, the US focused on domestic affairs such as Women's Suffrage and the Prohibition Movement. The 1920s brought strong, but not unparalleled, economic growth to the US as Europe rebuilt, only to fall into the Second Great War in 1939. Meanwhile, the US enjoyed two decades of domestic peace, with newspapers desperate for any interesting event, even the short 1925 Scopes Monkey Trial in which Clarence Darrow successfully defended the teaching of evolution on grounds of Free Speech.
Although giving aid to Allied Powers, the United States would remain out of the war until 1942, despite public outcry over 1941's British Landing where German troops devastated southern England before finally being rebuffed in a reversal of Dunkirk. Japan, which had conquered nearly unchecked in the Pacific through the 1930s (such as its speedy defeat of the Philippines), would draw in America with its Invasion of Hawaii on June 2, despite continuing guerrilla combat in British Australia. Eventually, Hitler's 1943 Operation Barbarossa would bring the USSR onto the side of the Allies, and GWII would be won with combined atomic arsenals of the United States and Soviet Union in 1945.
In reality, General Arsenio Linares did not reinforce San Juan Hill, meaning only 760 Spanish troops held the heights against nearly 15,000 Americans and 4,000 Cubans. The Americans won the decisive battle handily, giving a great deal of positive press for the war as well as young Colonel Roosevelt, who would eventually be given the Medal of Honor. With TR's gusto, skill, and fame, the Republican party would add him as vice-president to the 1900 ticket with McKinley.