States already do things like bar felons from voting and only put on 3rd party candidates that meet a certain signature threshold. Or add barriers to voting, like restricting when you can vote and ID laws.
For anyone wondering if the wording of the Constitution is unclear, this is the provision that constitutionally bars trump from office:
"No person shall be a Senator or Representative in Congress, or elector of President and Vice-President, or hold any office, civil or military, under the United States, or under any State, who, having previously taken an oath, as a member of Congress, or as an officer of the United States, or as a member of any State legislature, or as an executive or judicial officer of any State, to support the Constitution of the United States, shall have engaged in insurrection or rebellion against the same, or given aid or comfort to the enemies thereof."
Here is Article 2 section 1, referring to the office of the President of the United States:
"The executive power shall be vested in a President of the United States of America. He shall hold his office during the term of four years,..."
Trump engaged in insurrection, violating the oath of office he took. As such, he is constitutionally ineligible to run for office.
My bad. I overestimated the ability of people on this website to infer subtext.
The last section of Amendment 14 explains why the Supreme Court was more or less correct in its interpretation before you edited your original comment.
The Supreme Court ruled that the provisions you cited are not "self executing". It needs to be enforced by an Act of Congress. You assumed that because it says that, therefore it works on its own without the need for anything else. That's not how the law works in the US.
The text of Amendment 14 §5 which are you so reluctant to post:
The Congress shall have power to enforce, by appropriate legislation, the provisions of this article.
Now tell me, is it not a reasonable interpretation of this clause that the terms of Amendment 14 may only be enforced by Congress and not anyone else.
Don't cite Amendment 10 here. It doesn't apply. This power is explicitly delegated to Congress.