There is an armed protest scheduled at our state capitol building on Sunday. I have friends who live on our local capitol hill, and I'm also trying to find vacant apartments, etc., they can stay in COVIDly-safely for the weekend. This is the literal definition of terrorism.
Back to the Fourteenth Amendment...
As with the other Reconstruction Amendment, the originalist interpretation takes its cues from the aftermath of the Civil War. The point of Section 3 is to prevent former Confederates from holding office in the (re-)United States government and attempting to rebuild the Confederacy from within. So the sedition spoken of in the Amendment could be considered limited in its intent.
Despite its being the supreme law of the land, there's little a private citizen can do to violate it. It's mostly a limit on what laws the government can pass and enforce. So with some possibly rare exceptions that I might think of later, only the government can violate the Constitution. Any action authorized by the 14th Amendment that would prevent Donald Trump from holding any future office would need to take the form of some branch of the government withholding its cooperation or assent in some part of the electoral process.
For example, a State could refuse to accept Trump for its ballot, citing the 14th Amendment. Or they could refuse to certify his slate of electors. Or the Congress could vote to disqualify his electoral votes.
The problem in all of that is the legally cognizable definition of what it means to "engage[] in insurrection or rebellion against the same [Constitution], or give[] aid or comfort to the enemies thereof." The Constitution doesn't define any of those terms. Under lesser U.S. law, those terms are defined, and in many cases the activities they represent are outlawed. But if we're going to use those definitions, then the President would need to have been convicted of one of those offenses. Or if not, by what other standard would he have been judged to have committed any of the acts that disqualify him? Due process means it can't just be the judgment of some random government functionary that Trump committed disqualifying acts.
One of the oldest and most important cases in American jurisprudence, Marbury v. Madison, held that a person elected to an office has a right to take that office. Unfortunately things didn't work out completely for Judge Marbury, but that part of the holding in his case is still valid. (The rest of the complaint was dismissed on standing.) But it means that whoever in the government, in his official capacity, acts to prevent an elected Donald Trump from taking his office has the burden of proof. If Congress disqualified Trump's eventual electoral votes on 14th Amendment grounds, he could sue the Houses of Congress (I believe in the DC circuit) and he would have the presumption of the right to office.
Similarly, while States may place reasonable administrative restrictions or limits on the declaration of candidacy for any office whose election they control, they may not otherwise disqualify candidates who meet eligibility requirements. The adjudication of whether Trump is eligible to declare his candidacy in a State, under the 14th Amendment, would therefore come in the form of a relevant State authority refusing the otherwise properly-filed candidacy papers, and then a suit in State court to determine whether the 14th Amendment bars his candidacy. And since such a suit would raise a "federal question," it would be reviewable in the U.S. Supreme Court, where Donald Trump might still have favor. If Trump had not been previously convicted of anything, he would enjoy the presumption of eligibility.
Section 5 is the kicker. It, like many parts of the Constitution, authorizes Congress to enforce by legislation the provisions of the Amendment. A court could easily find that the Congress has done so, in the form of laws defining crimes for sedition, giving aid and comfort to the enemy, and so forth. That standard having been set, a conviction on one of those charges may be required in order for it to properly authorize any government officer to invoke the 14th Amendment.
But maybe Congress never intended those to be the implementation of the Amendment. And we have to consider that Victor Berger was refused his seat in the House (and did not choose to invoke Marbury), merely because he was under indictment for crimes that stemmed from disqualifying acts. (He was later convicted, but the House acted before conviction.)
As I said, turbulent, uncharted waters.
