By James Finck, Ph.D.As a political historian, I was disappointed when Joe Biden backed out of the presidential race. I say that for no other reason than it’s been a rare occurrence in history where we have had two presidents battle it out.However, while it would have given me plenty to write about, a president-on-president fight would not have been unprecedented. It has actually happened twice before, but it’s been 112 years since the last time. It does not mean having Kamala Harris, a sitting vice president, taking on former President Donald Trump does not have its own historic significance.It may sound surprising, but a president versus vice president election has only happened three times in America. And, historically speaking, those circumstances are even more intriguing. Whether its president versus president or president versus vice president, these are interesting elections in that in most elections one candidate runs on their record while the other runs on promises. However, as with the six previous elections, this year both candidates must defend their record.The first time two presidents squared off against one another was between Grover Cleveland and Benjamin Harrison in 1892. Cleveland first won in 1884 only to lose to Harrison in 1888. Jump ahead another four years, however, and voters regretted their decision. 1892 saw the same two candidates, and this time voters corrected their mistake by reelecting Cleveland for his second term, making him the first president to serve two nonsequential terms.The other president v. president battle, not discussed as much, possibly because neither ex-president won, was in 1912 but the story began in 1900. That year, Republicans ran incumbent President William McKinley, but with slipping approval ratings the party decided to change up the ticket and run newly celebrated war hero Theodore Roosevelt as VP. Long story short, McKinley was assassinated, and Roosevelt became the new chief executive. TR, an extremely popular president, easily won reelection in 1904 but decided not to run in 1908.One reason he stepped down was that he basically handpicked the next president, William Howard Taft, who basically ran on Roosevelt’s coattails and platform. Roosevelt felt his new progressive reforms were in safe hands and went to Africa to hunt lions. Taft, however, did not turn out to be the reformer TR hoped for, and in 1912 he came back ready to resume his old job.The problem was Taft was not ready to relinquish ...