The election of 1876, where the winner came down to who won three contested Southern states (Florida, South Carolina and Louisiana) is probably the clearest example, as for a while nobody truly knew who had won between the Republican Rutherford B. Hayes and Democrat Samuel Tilden. Republicans charged that Democrats were endeavoring to steal the election through violence and terrorism against African American voters, while the Democrats said that the ones stealing the election were the Republicans. The election resulted in an electoral crisis that, at the time, many feared would result in a second Civil War. Here's an excellent answer by u/indyobserver examining that election in detail, and, as a bonus, talking of the 1800 election too.