We’re about to witness a political first. When 20 Democratic presidential hopefuls take the stage in Miami tonight and tomorrow night, it will be the largest number of candidates to ever participate in a party’s presidential debate. The field is so big that the debates must be stretched over two nights to accommodate all the candidates.

When Democrats debate one another, drama always waits in the wings — so it’s worth looking at how we got here. Democratic presidential debates are actually a relatively recent phenomenon.