What major historical event happened between the first poll and the second poll

Alfred London a Kansas governor was perceived by the poll, to be in the lead against Roosevelt.

Explanation:

There was a presidential election in 1936 whereby of 1936 Alfred Landon, a Republican governor in Kansas vied against the incumbent President, Franklin Roosevelt. In the 1936 election, the Prediction and the perception was that Landon would get more than 57% of the total vote against Roosevelt's who was perceived to have around 43%.

The statistics provided such an implication.