President Joe Biden announced his candidacy for re-election this week, with a plan to make the 2024 election a referendum on Donald Trump rather than his first-term policies. Though Biden has accomplished a great deal in his first term, what motivates voters most is the fear of what might happen if the other candidate wins. This is true for both Republicans and Democrats. The president plans to follow this strategy, and he wouldn't be the first to do so. Previously, George W. Bush ran for re-election in 2004 by targeting John Kerry, and Harry Truman won re-election in 1948 by running against the "do-nothing" Republican Congress. Biden has an advantage over those presidents, as he is expected to run against a former president who is quite unpopular, particularly among independents. If Trump is the Republican nominee, Biden will be the first president to have run against a former president in over a century. Therefore, there are very few Americans who don't have already established opinions about the former president.