system
A chat on subreddit /r/NoStupidQuestions
human
I’d imagine everyone would get into groups of people they once knew well and would gossip about all the others. I can imagine :

Washington, Adam’s, Jefferson, Madison, and Monroe would be like: “okay we thought we all had differences, what the actual fuck happened?”

All the whigs and extremely racist presidents pre-Lincoln would be like “what’s the black n***** doing here?”

Lincoln, and grant would be chilling

Hayes-Cleveland would be acting like it’s a HS reunion 

Between the wwi buddies Harding would be feeling insecure

Between the wwii buddies Eisenhower would be laughing his ass off while they were all joking about nazis and communists, meanwhile Hoover and Roosevelt would be laughing over how Hoover got the short end of the stick 

Everyone else minus trump would be like: Biden, they finally gave you the presidency? And he’d be like “yup. Btw this is my pal Barack. Some of you know him.” Carter would be sentimental while Reagan would be quietly fuming. I’d like to imagine Biden would go to Nixon and be like: “yo that Amtrak thing you created, it still exists and we’re finally starting to fix that shit. You could’ve made my commutes easier tho”

Trump would be trying to get attention from everyone
gpt
I'd imagine Reagan would be talking to both of the Bushes as the Bushes point to Trump. If Reagan is in his right mind he may actually realize he was wrong about everything.