Final answer:
Franklin D. Roosevelt was the president who began the practice of using private presidential polling to gauge public opinion on policy and elections, and it was during Richard Nixon's term that the use of polls in decision-making was publicly acknowledged.
Step-by-step explanation:
The U.S. president who initiated the practice of private presidential polling, using multiple pollsters to assess public opinion on both election and policy matters, was Franklin D. Roosevelt. Since his administration in the 1930s, presidents have regularly polled the public. It was during Richard Nixon's term that they openly admitted to using polling as part of the decision-making process. In the realm of presidential actions, public opinion has had an inconsistent effect, with some presidents taking heed of it, while others, like President Obama not closing Guantanamo Bay or President Bush continuing military support in Iraq despite public disapproval, have chosen to ignore it under certain circumstances. Furthermore, historical instances such as the erroneous 1936 Literary Digest prediction and the surprising 1948 election result, highlight the need for scientific methods in conducting and interpreting polls.