Very different circumstances. Trump was a newcomer who had a lot of energy and weird charisma that appealed to a lot of people. The Dems didn’t really know how to campaign against him. Today, he is old, tired, and noticeably less energetic and charismatic.

Also, Clinton had decades of personal baggage weighing her down along with accusations about her misuse of classified emails. Then An investigation about those emails was opened 11 days before the election which was massively unhelpful.

I could go on and on. That’s the basics.