Lichtman is best known for the "Keys" system, presented in his books The Thirteen Keys to the Presidency and The Keys to the White House. The system uses thirteen historical factors to predict whether the popular vote in the election for President of the United States will be won by the candidate of the party holding the presidency (regardless of whether the president is the candidate). The keys were selected based on their correlations with the presidential election results from 1860 through 1980, using statistical methods adapted from the work of geophysicist Vladimir Keilis-Borok for predicting earthquakes. The system then correctly predicted the popular vote winner in each of the elections since 1984. In 2000, he inaccurately predicted, using his system, that Gore would be the next president. Lichtman has provided commentary for networks and cable channels such as CNN, MSNBC, and Fox News. In the 2016 election Lichtman predicted that Trump would win the popular vote; Trump ended up losing the popular vote (while winning the electoral college). In August 2020, Lichtman announced the model's prediction that presumptive Democratic Party nominee Joe Biden will be elected president.