You are right. /s/ Here is a good example: <<Representatives and direct Taxes shall be apportioned among the several States which may be included within this Union, according to their respective Numbers, which shall be determined by adding to the whole Number of free Persons, including those bound to Service for a Term of Years, and excluding Indians not taxed, three fifths of all other Persons>>. If you choose to reply to this post, please carefully consider how Black and Brown Americans would feel knowing this was deeply embedded in this history of their country's founding document. (It is horrible!)

This segment is widely called the "Three-fifths Compromise" in American English. It refers to the fact that enslaved people would be counted as 3/5 of a person for the purpose of determining gov't representation.

From a modern perspective, this section is wholly demented and supports the institution of slavery. This support for the institution of slavery in the founding document of the United States is a terrible stain upon its reputation.

The biggest issue I have with the US Constitution in a modern society: It is too hard to change. (When is the last time the US had a serious effort to pass a new amendment? 1970s / 1980s-ish: Women's equality, but still it failed!) Many successful, younger democracies have found ways to allow non-extremist changes to their constitution, to support "futurism" (my own term) -- the progression of society. Personally, I am a big supporter of regular (frequent), small changes to a country's constitution to support, and facilitate, social change.

There are four major structural issues I can think up off the top of my head (this is unfair — we're discussing my wife's job):

1. Modern gerrymandering is probably the Achilles heel that'll bring the US to its knees.

2. Judicial capture is the standard playbook for autocratic take-overs of democracies — there needs to be a reaffirmation process & it needs to be a "yes - no > 1/2*senators".

3. The electoral college is particularly vulnerable to bad actors at the state level, and the opportunity cost to capture the college is higher than the capture cost.

4. The Senate, itself, was a known-to-be-bad compromise to build a confederation, rather than a formal union into a single, sovereign State.

I'm not entirely convinced of the last one: I kinda like the idea if 50 separate competing democracies all trying to come up with great ways to be a state, with a fairly low barrier-to-migrate.

I truly can't think of a more fundamental element of a democratic system than who is enfranchised, and there have been two or three enormous changes in the answer to that since the founding.