Today’s pundits might be making the same mistake with Trump’s 2016 coalition. Throughout the Mueller investigation, the impeachment process, the pandemic, and record unemployment, Trump’s approval rating in the RealClearPolitics average has remained surprisingly consistent (around the mid-to-low 40s), showing that at least 4 out of 10 people support the president regardless of whatever the opposition throws up. That may not be sufficient to guarantee victory, but it’s a precious asset in a general election — especially with Democratic enthusiasm for Biden comparatively low.
The second factor is that people often vote for incumbent presidents based on certain intangibles (leadership skills or likability) despite the candidate’s perceived flaws or policy disagreements. The Washington Post alluded to this phenomenon after Truman’s victory: “The American people admire a man with courage even though they don’t always agree with him.” The voters might even give the opposing party control of Congress during the midterm elections to check that president, but they will still reelect a flawed incumbent because of their supposed charisma (see Bill Clinton and Barack Obama) or boldness (see Truman).
Like Trump, Truman was seen as a fighter who was not afraid to go against the political establishment. And like Biden, Dewey was an uninspiring candidate who, because of overconfidence, played it safe and limited his public appearances.