It’s a long list, but the long lasting bit was his incompetence and failure to fully staff the government made it impossible to function properly. Note, federal government workers are located nationwide, not just the capitol. Plus with the top secret docs he stole, some of which had information on the nuclear capabilities and defenses of one of “our” (US) allies, that’s a whole other mess.

As for the consequences, that’s still panning out. Lots of fraud cases, for example. Some think Hamas was able to attack, because it was Israel’s defenses that were in the leaked secret documents, but that has not been confirmed and is just gossip.

Denying the existence of the pandemic until it was already bad here led to way more people dying than what was unavoidable.

That’s not even touching on the amount of debt he accrued, foreign policy dealings, or general behavior.

No shame in asking. Half of Americans pay no attention to voting at all, and many here would ask the same if not so emotionally intense a subject.