It originated on the Chapo Trap House podcast (e.g. in the thumbnail of this video). Not sure when the earliest use of it was, but it was at least early 2019 from a quick search through Will's twitter. It refers to how Trump's photos show, or at least used to show, him as slightly moist, damp, or sweaty. A slight sheen of water seemed to be on him at all times, like some fucked up amphibian. Compare this to the eternal dryness of other politicians like Biden.

He's damp, dank, and dripping. He's soggy, he's gushing, and he's moist. He's dewy, he's soaked, he's sopping.

He's irriguous, he's saturated, he's clammy.

look at him, he's constantly dripping

He's a sweaty mother fucker

He's such a soggy-bottomed bastard that Cap'n Crunch has a vendetta against him

what's the ploblem?

Moist

he is

he is very big and very wet