They'll stop loaning us money. Think about what happens then.
The Chinese have already pretty much stopped buying US treasuries. They are trying to dump the bonds they have.
Most of the deficit is financed by digital money printed/created by the Federal Reserve to monetize debt bought by their member banks from the Treasury department. And those member banks are told they must buy treasuries if they want the negative rate financing.
China is not so much needed anymore to finance the US government.
But the idea of boycotting China would lead to hyperinflation in many consumer goods. Walmart especially would cringe in pain.