US stocks got slammed on Tuesday, dropping more than 800 points as doubts mounted about the US-China trade truce that was struck over the weekend.

Investors fretted that the 90-day cease-fire negotiated by President Trump might not be what it was billed as, as Trump unleashed a threatening tweet Tuesday morning.

“President Xi and I want this deal to happen, and it probably will. But if not remember, I am a Tariff Man,” Trump tweeted.

The Dow Jones industrial average was recently off 805.35 points, at 25,021.08, with the selloff erasing last week’s gains on fresh optimism about the US-China trade war.

This weekend, Trump had announced that the US was postponing a planned Jan. 1 tariff hike, to 25 percent from 10 percent, on $200 billion worth of Chinese imports.

That had sent the Dow up 287.87 points on Monday, to close at 25,826.43.

But on Tuesday, traders fretted increasingly that details about the start date of the truce have been murky. Markets also got rattled when Trump appointed US Trade Representative Robert Lighthizer, a China hardliner, to lead discussions in Beijing.

“We didn’t see Trump follow through,” Quincy Krosby, chief market strategist at Prudential Financial, told The Post.

“This is the market saying we need a little bit more in order to feel optimistic,” Krosby added.

Also adding to market jitters was a shift in the bond markets that signaled a potential economic slowdown.

Yields on 2-year Treasury bonds were higher than 5-year bonds, flashing a warning that market risks are higher in the short term.

The phenomenon, known as an inversion of the yield curve, tends to precede recessions.