actual reason for the error was that the Literary Digest relied on voluntary responses. As the article explains, the 2.27 million "respondents who returned their questionnaires represented only that subset of the population with a relatively intense interest in the subject at hand, and as such constitute in no sense a random sample ... it seems clear that the minority of anti-Roosevelt voters felt more strongly about the election than did the pro-Roosevelt majority." A more detailed study in 1988 showed that both the initial sample and non-response bias were contributing factors, and that the error due to the initial sample taken alone would not have been sufficient to predict the Landon victory. The magnitude of the error by the Literary Digest (39.08% for the popular vote for Landon v Roosevelt) destroyed the magazine's credibility, and it folded within 18 months of the election, while George Gallup, an advertising executive who had begun a scientific poll, predicted that Roosevelt would win the election, based on a quota sample of 50,000 people. His correct predictions made public opinion polling a critical element of elections for journalists, and indeed for politicians. The Gallup Poll would become a staple of future presidential elections, and remains one of the most prominent election polling organizations. Campaign Landon proved to be an ineffective campaigner who rarely travelled. Most of the attacks on FDR and Social Security were developed by Republican campaigners rather than Landon himself. In the two months after his nomination, he made no campaign appearances. Columnist Westbrook Pegler lampooned, "Considerable mystery surrounds the disappearance of Alfred M. Landon of Topeka, Kansas ... The Missing Persons Bureau has sent out an alarm bulletin bearing Mr. Landon's photograph and other particulars, and anyone having information of his whereabouts is asked to communicate direct with the Republican National Committee." Landon respected and admired Roosevelt and accepted most of the New Deal but objected that it was hostile to business and involved too much waste and inefficiency. Late in the campaign, Landon accused Roosevelt of corruption – that is, of acquiring so much power that he was subverting the Constitution: Franklin Roosevelt's most notable speech in the 1936 campaign was an address he gave in Madison Square Garden in New York City on 31 October. Roosevelt offered a vigorous defense of the New Deal. The most memorable section of the speech was, in the opinion of most observers,