It goes back to FDR and one of his fireside chats on July 24 1933:

After the adjournment of the historical special session of the Congress five weeks ago I purposely refrained from addressing you for two very good reasons. First, I think that we all wanted the opportunity of a little quiet thought to examine and assimilate in a mental picture the crowding events of the hundred days which had been devoted to the starting of the wheels of the New Deal.

Secondly, I wanted a few weeks in which to set up the new administrative organization and to see the first fruits of our careful planning.

He was referring to the first 100 days of the 73rd Congress rather than his own Presidency, but those dates are the same, and the progress FDR made in his first 100 days was so immense that the media started comparing every other president to his performance.

In FDR's first week, he shut down the banks (which were on a run) for four days to pass the Emergency Banking Act, which introduced federal deposit insurance. When the banks re-opened, people queued up to put their money back into the banks. This gave the US a financial stability it had not had for a long time. For the rest of the 100 days, he introduced the Fireside Chats - weekly radio addresses from the White House. These calmed the public down after a tumultuous few years. He kicked off the New Deal, setting up FERA (forerunner of the WPA and Social Security), the CCC (which paid unemployed men to plant trees, mitigate soil erosion and fight wild fires), the AAA (which raised agricultural prices, allowing farms to modernise and even helped pay some destitute farm mortgages) and the TVA. He also passed NIRA, which improved workers' conditions and safety, outlawed child labour, and set up the PWA which further reduced unemployment while contributing much needed infrastructure.

These programmes and laws had a lasting impact and were the point the US turned the corner from the fear and chaos of the Great Depression towards the sleeping giant that would become the world's first superpower little more than a decade later.