The entire logic of the constitution is for a Republican government (we call that a representative democracy today.) It was violated twice for short term pragmatic reasons - one by letting white slavers have more votes than other people and by letting small states have as many senators as big ones.
The first gave Southern states disproportionate power in our first decades, and when free people finally sufficiently outnumbered its tapeworm society, they left violently.
The second worked well enough so long as differences between the states were not too severe. Now that so many Americans, disproportionately in smaller states, are dominated by those who seem to want us to be a Christian Iran, the senate has become a poison pill for the country due to its artificially enabling a minority to tyrannize over a majority.
Both violations of the constitutions internal logic work when cultural issues are not divisive, and make it unworkable when they are. When the Senate’s shortcomings in republican terms are added to gerrymandering of the House and an Electoral College that works to defeat the majority, it may yet destroy the country.