You don't see presidential candidates who are less than 35 years old or who are not US citizens by birth because those qualities are required by our constitution. Thanks to former president Trump there is another constitutional requirement that applies to presidential candidates that needs to be considered this cycle.
The 14th Amendment, Section 3 of the US Constitution makes it clear that a former office holder who has taken an oath to defend the Constitution and then participates in an insurrection or gives aid or comfort to a participant is disqualified from holding office. The 14th Amendment does not specify the criteria for imposing disqualification. It also does not require the legal standard of proof beyond a reasonable doubt or a conviction. We may eventually want an amendment, law or Supreme Court ruling to make this more clear, but for now we are faced with an immediate need and the Constitution provides a solution.
One obvious answer of who would enforce this requirement and decide what criteria they would use might be the person or offices in each state who would determine if a candidate meets other requirements to be on the ballot (such as age and citizenship). I think the person who makes those decisions in most states is the Secretary of State.
Another option is a court ruling. A court in Colorado was asked to remove Trump's name as a presidential candidate from the Colorado ballot. The judge agreed that former president Trump “incited” the January 6, 2021 riots and backed that with evidence including testimony given to the House January 6th Committee.
After clearly stating that former president Trump had participated in an insurrection, the judge accepted the defense claim that the presidency was not an office as required in the amendment. The judge agreed that if the authors of the amendment intended for it to apply to a former president they would have explicitly said that. The judge then refused to remove Trump from the ballot.
Granted that the amendment wording is very vague, but that sounds like a judge searching for a way to not remove Trump's name from the ballot. This will have to go to the Supreme Court and would have even if the judge's decision had gone the other way and had removed Trump's name from the ballot.
The most important thing is the judge clearly said former president Trump had participated in an insurrection. Of course, the January 6th Committee also proved he incited an insurrection. I would argue there is stronger and more timely proof that Trump incited an insurrection.
Former president Donald Trump was
impeached by a bipartisan majority in the House (including ten
Republicans) for “incitement of insurrection”. Although there
were not enough votes in the Senate to convict him, there was a
bipartisan majority in the Senate (including seven Republicans) who
believed he was guilty as charged. Every Representative and Senator
who voted to impeach or convict knew that their vote would not remove
former president Trump from office. President Biden had already been
sworn in before the final Senate impeachment vote. However, their vote did
show they believed former president Trump had participated in an
insurrection and should not be allowed to be president again (impeachment conviction means the person is removed from office and disqualified from holding office again). Their votes had nothing to do with the 14th Amendment, but they clearly declared he had participated in an insurrection and should not be allowed to serve again.
I believe the bipartisan majority votes for impeachment in the House and Senate are enough by themselves to satisfy the constitutional requirement to disqualify former president Donald Trump from becoming president again on a national basis, not just the state level. As I said, this will need Supreme Court approval, but a clear reading of the text should support his disqualification.
I hear a lot of claims that Trump's fitness to hold office again should be decided by voters. I'm sympathetic to that claim, but the 14th Amendment was written after the Civil War to prevent southern sympathizers from electing people to offices in a government they violently tried to destroy. That sounds close to the situation we face today. We have a large segment of the citizens who seem very willing to re-elect a man who lies that the last presidential election was stolen, incited an insurrection, tried to overthrow the validly elected government (as certified by all state governments and many court cases) and continuously brags he will take unconstitutional actions if re-elected. The 14th Amendment is still in the Constitution and until it is revised or revoked we should use it to counter a charlatan who seriously threatens our country.
Text of the 14th Amendment, Section 3, to the United States Constitution
“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.”
The highlights are mine.