If some drunk at a bar jumps up and declares himself Emperor of Scotland, has he made a coup attempt?
If a mob of football fans trash city hall, then take some selfies and wander off, have they attempted to undemocratically wrest power from the government?
Seizing is an action verb with a clear meaning. Power, in this context, has the clear meaning of political power. While the Trumpsters did a lot of unforgivable things, they didn't attempt a coup. And yes, I think the credibility of the threat factors in. Just for dignity's sake, if nothing else.
Come to think of it, that might be why I'm digging in so hard on this. Calling this bufoonish slobbery a legitimate coup attempt makes them sound more intelligent than they are. Perhaps it's just a visceral rejection of the suggestion that they have human intelligence.
Nonetheless, I'll keep holding them to a higher standard of punishment than most here, without affording them the dignity of a political aim. They are just imbeciles being imbeciles.
Eta: actually no, so I may be missing the context. Sounds like that's actually out of the Hitler playbook, though: Keep repeating a lie till people start to believe it.