In a 2013 paper, “Substituting the End for the Whole: Why Voters Respond Primarily to the Election-Year Economy,” Andrew Healy of Loyola Marymount University and Gabriel S. Lenz of the University of California at Berkeley examined annual personal income growth across presidential terms. Across Clinton’s first term, personal income growth was moderate overall, but strongest in the critical fourth year. Carter had the opposite experience, with the worst year arriving at the end: Personal income growth actually declined in his final year in office. Even though Carter oversaw higher cumulative income growth during his full term (6.9 percent, vs. 6.2 percent for Clinton), he lost his bid for reelection, while Clinton won easily.

That outcome is consistent with how voters have judged incumbent presidents in other elections. “Voters are myopic,” Bartels and Achen write in their book, Democracy for Realists. “The performance of the economy over the course of a president’s entire term—which provided a better measure of changes in voters’ welfare, and presumably provides a more reliable benchmark of the incumbent’s competence as well—is almost entirely discounted by voters when they go to the polls.”

The question now is how bad the economic fallout will be and what government officials, including Trump, can do to curb its effects.