The Pendleton Act did not break up the power of political machines to any great extent. The law was simply not wide-ranging enough to do so, particularly in the short term.
The Pendleton Act was meant to break up the “spoils system.” It took federal government jobs and put them under civil service rules. That meant that people had to be appointed to those jobs on merit, not on the basis of political connections. It is conceivable that such a law would have weakened political machines, but it did not. There were still political machines long after the Pendleton Act was passed. For example, President Harry Truman got his start in national politics when he was elected to the Senate in 1934. He won in large part due to the support of the Pendergast machine in Kansas City.
Let us look at two reasons why the Pendleton Act was not more effective. First of all, it did not cover many jobs in the federal government. At first, only about 10% of all jobs in the federal government were converted to civil service jobs. This was not enough to break the machines. Second, and more importantly, the act did not cover the state and local governments. It was state and local jobs that were really important to the political machines. Therefore, the Pendleton Act did not really get very close to threatening the existence of the machines.