That would be an incredibly risky escalation, and it would be a stupid ultimatum to issue.

The people, or even states, could escalate in response. The worst case is escalating to violence; ICE isn’t trained, equipped, or numerous to deal with deploying into a violently hostile area. The army could, but then we’re in full blown civil war.

A more realistic middle ground is that it pushes people or states into nonviolent non-compliance by eg refusing to pay federal taxes. Frankly if California and New York alone stopped paying federal taxes the system would probably crumble.

Yeah because that works out really well in history!

That's not how the political reality of exacting mostly voluntary compliance from the masses works.