Do they ever provide any historical support for this claim?
I ask because the latest example of a Constitutional Republic is the United States of America, which has lasted more than 200 years, and is now being transitioned into a socialist, Marxist nation through anarchist actions created by socialists and Marxists.
What do we call a “Constitutional Republic in Name Only”? A very bad turn was taken after the so-called Civil War. We have been bitter clingers to Past Glory for at least 100 years now. We have been “transitioning” a lot longer than you may think.