It should be noted, during the early Twentieth Century, the United States government took on a more significant and active role under the Progressives. Theodore Roosevelt, for example, was famous for his efforts in prosecuting big business operations (furthermore, it should be noted that his successor, Taft, was far more active in prosecuting big business than Roosevelt himself had been). Later, government would take on still greater power for itself, with the advent of World War I and the requirements of coordinating a wartime economy.
After the end of World War I, there was a reaction against this increase in government power represented by the Progressives and, later, the First World War. Thus, in the 1920's, Republican presidents, starting with Warren Harding, restored a policy of laissez faire economics, which eschewed government regulation of the economy. However, the Great Depression made laissez faire untenable. The election of Franklin Delano Roosevelt signaled a profound shift towards the political left, with a far more powerful and interventionist federal government than had ever previously been seen in US history.
Roosevelt advocated for deficit spending, and under the New Deal, federally funded organizations and agencies were created, aimed at providing relief and getting people working again. Under his leadership, the government also famously imposed an audit of the banking industry in order to stabilize that sector of the economy. New regulatory measures and safeguards were put in place (such as the FDIC, which insured savings accounts, or the SEC, which regulated the Stock Market). Additionally, as part of the New Deal, the US government would adopt a system of social security for the first time. These are only a few examples. There are many more you can point to.