Constitutional republic means elected by the people.
The Soviet Union had elections. Iraq under Saddam had elections.
The conclusion above that we need to “vet” our candidates is a pretty low bar. Isn’t that what campaigning is?
The constitution does not define what kind of economic policies or social safety nets the country should have. That’s why Bernie Sanders and Mandami the Commie can get elected and serve.
In the interest and spirit of the Preamble it seems prudent to make a distinction between advocating this or that form of government, and holding public office to affect changes that undermine the body.