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.