Political scientist Larry Sabato has this chart showing the recent history of major party decisions to reduce the number of presidential primaries and caucuses. Democrats canceled some in 2012, and Republicans did in 2004. However, in those years, no one who had ever held public office was running against the party’s incumbent president, and in many primaries, only one person (the incumbent president) had qualified for the ballot.

By contrast, in 2020, two former Republican Governors would like to run against President Trump in Republican primaries, so in that sense, the effort by some Republican Parties to eliminate primaries and caucuses is unprecedented. Thanks to David Sturrock for the link.