After Spanish-American war America was posed with a question: to take the Philippines and various other remnants of the Spanish empire or not. The Treaty of Paris (1898) that was ratified by the senate in a narrow 57-27 (just two votes shy of failing) led the US to obtain Guam, Puerto Rico, Cuba and the Philippines for $20 million in wake of the US military defeating Spain.
This was a turning point in American history because America now would be an empire with colonies. If the treaty had failed then much of World History could have changed. If America never became an empire then perhaps America would never have any intention of involving itself with the European conflict in World War 1. Which would not of have created the Treaty of Versailles which in part caused The Second World War sparing millions upon millions of lives.
The treaty was close to not passing. The treaty could have been rejected had the then Democratic party front runner, William Jennings Bryan, not had supported the treaty. Bryan was the previous Democratic presidential nominee and represented a new wave of populism that supported ‘free silver’. He wanted the gold standard to be broaden to the gold and silver standard to help debt ridden farmers. Despite his staunch anti-imperialism, he supported the treaty and swung many populist senators votes.
The reason for his support is not truly known. Bryan said that he supported the treaty because he thought the various islanders would be better off in the hands of America than in Spain. However, some speculate that he thought the treaty was going to fail and did not want to support a failed treaty. That would look bad in the upcoming presidential campaign that he eventually did get nominated (but lost).
The estimates of how many senators Bryan influenced range from about half a dozen to a dozen. Clearly enough to reject the treaty and stave America off the path of empire. The political pressure that were possibly on Bryan got the best of his principles and he let the US go on the path to empire.
Always stick to your principles. You do not win by giving in.