Many said he was qualified, but others disagreed. In the press. There was no lawsuit.
If I understand this thread correctly, there is no legal way to enforce disputed presidential qualifications in the courts, regardless of whether the dispute is over age, birthplace, residency, or adherence to a prior oath to the Constitution. A challenge to qualifications can be dismissed, as happened when Barack Obama faced a birther lawsuit. But, unless SCOTUS shocks everyone with a totally unexpected ruling, it seems there is no way to prevent an oath-breaking insurrectionist, or a native born Canadian, from being nominated. And it defies all understanding to think you can stop the winning nominee from taking office.
If so, this is a defect in our system of government. And, while a future progressive-dominated Congress could pass a law telling the court change their approach here, I don’t see how it could really be fixed except by SCOTUS. If Trump wins, and turns out to be as bad as most here expect, the justices probably will learn the lesson and act differently next time. There is nothing I see, in the SCOTUS oath of office, preventing that.
As for preventing Trump from being nominated being undemocratic, while SCOTUS is right to consider that, if you disqualify the candidate long before nomination, there is no sense in which policy was dictated. The GOP can, if Trump were disqualified, nominate someone with the same political positions. They can nominate an otherwise qualified insurrectionist. They just can’t nominate someone who is disqualified.
Does that make enforcement of Section 3 unimportant? After all, Trump Jr. is, AFAIK, legally qualified. And he’s no less danger than his father, right? Wrong. He’s probably less dangerous, because a first term president, lacking prior government experience, won’t do as much damage to the republican system of government as someone who worked in the government before. So even if I don’t have as big of a personal revulsion regarding oath-breaking as the radical Republicans did, I still see wisdom in Section 3 being enforced, as written, so longer as SCOTUS steps up early in the nomination process.