States have always had that power. Whether its age, naturalization, or oath-breaking, it's never been up to the federal government to decide disqualification.

States remove federal election candidates for eligibility reasons all the time. Trump is yet again getting special treatment.

Arguably states unilaterally removing a candidate from the ballot is a major paving stone on the road to the civil war, when Lincoln won because of the split pro slave vote the south blew a gasket because it only just hit them then that everyone else had enough electors among them to ignore the south completely.

It's not a State Law they're using to remove him. It's federal election laws. It's in the Fourteenth Amendment to the United States Constitution which was adopted on July 9, 1868, as one of the Reconstruction Amendments. They even specifically discussed if a President should have an exception and decided it did not. The Supreme Court is choosing NOT to enforce the US Federal Constitution!

On the other hand, I could definitely see a bunch of red-controlled states deciding to remove Biden (or future Dem candidates) for whatever bullshit reason in the future, so while this ruling isn't necessarily consistent with current practice it at least doesn't open the door to that.

Except that R's are already pretty cool with being inconsistent about what is our isn't allowed, which is how we got certain members of the SC in the first place...