I was a close observer of American presidential election disputes in 2000, 2004, 2016, and 2020.
If you do not know the history or your memory is rusty, you might review:
video clips and documentaries on the 2000 election;
video clips and documentaries on the 2004 election;
video clips and documentaries on the 2016 election.
A good project for students would be to study each of those elections, debate the results, and whether the electoral college is a good thing or a bad thing. There are definitely two sides to the issue, and political hyper-partisans tend to take different positions not on principle but based on whether they think their candidate should win or lose.
Unprecedented in modern times, of course, is the failure in 2020 of the losing candidate, Donald Trump, to refuse to concede the election after his appeals were denied by dozens of courts, and even after Congress certified the results in each state.
That said, disputes are bound to happen again as long as the electoral college remains in place and candidates can win national elections by millions of vote but lose the electoral college count by 18,000 votes or less.
Preserving the republic: “In 1787, Ben Franklin said that our founders had created “a republic, if you can keep it.” More than a monarchy or dictatorship, a republic depends on the goodwill, patience and shared values among citizens. The events of the past week tested that.” — 60 Minutes.