The issue in CO and elsewhere is whether or not the 14th Amendment bars an insurrectionist from running for / being President. The 14th Amendment is part of the US Constitution. Some amendments have relied on court cases to hold that they apply to the states, but parts of the 14th Amendment state explicitly that it applies to the states, and in any case Section 3 of it also refers to "under the United States, or under any State" when it proscribes an insurrectionist from holding a federal or state office.

Section 3

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. But Congress may by a vote of two-thirds of each House, remove such disability.

There are two issues here with regards to Grump:

1) Was he “engaged in insurrection or rebellion against the” Constitution, after having “taken an oath…to support the Constitution”?

First off, yes he did take an oath to support the Constitution when he was first sworn into the Presidency.
Now he hasn't been convicted by Congress (he was impeached, but not convicted) or by any court of insurrection, but probably a court has a right to make that determination for itself. As well, the 14th Amendment doesn’t mention a need to be convicted or adjudged by any court, but rather simply to have “engaged” in insurrection is enough to trigger the prohibition. Anyway, the CO courts decided that they had the right to declare him an insurrectionist.

2) Does the 14th Amendment proscribe an insurrectionist from being the U.S. President?

The issue there is that while the 14th Amendment specifically proscribes someone from becoming a Senator or Congressman, or elector of the President and Vice-President, it doesn’t specifically state that an insurrectionist may not be THE President, other than by way of the probably all encompassing proscription to “hold any office, civil or military, under the United States, or under any State” where it would seem that “any office, civil or military, under the United States” would include the office of the President.

Still, some people argue that if the Framers intended for the 14th Amendment insurrection clause to apply to the President it would have stated so explicitly and others argue that the history of the revisions of the 14th Amendment and its background of why it was written after the Civil War to keep insurrectionists out of office, support that it was intended to apply to the President. But most say simply that the plain language “hold any office” also applies to the President.

In any case, the one real world example we have is Jefferson Davis – he was a Senator before the Civil War and took an oath to uphold the Constitution, then led the South in insurrection against the United States, and was barred from ever being President by the 14th Amendment. Most would say that Grump is equally barred from being President, especially if he is ever convicted of insurrection.

As far as what I have heard at least one person saying about how the federal government should just leave the states alone to elect the President in all respects, Article II of the Constitution itself outlines exactly how the President is to be elected, it leaves open to the state legislatures how to elect their electors (based on the number of congressmen that state is entitled to in the US Congress), but those electors then are governed by the US Constitution as far as their voting for the President process.

Keep in mind that we are a Republic, not a Democracy, and we don’t elect the President directly – the electors whom we elect, do. The people in each state elect their electors, but then the electors go on to elect the President. This, most say, is because at that time the Framers didn’t think the American people were smart enough to elect their own President, at least not directly.

So, this outlier argument falls short there in two respects - one is that the states don't elect the President not directly anyway, and two, the Fourteenth Amendment does apply to the states. So if it is decided that the Fourteenth Amendment applies to preventing a former President like Grump from holding the office of President ever again if he is held to be an insurrectionist, then the individual states would have to be stopped from sending up any electors who could potentially vote for Grump.