I suspect an offense against the USA would be easy to pull off.

I suspect nothing in war is ever easy, and something the size of the US comes with certain operational challenges. Establishing air superiority would be difficult, for instance, and without it, transporting troops, supplies or equipment over longer distances is difficult. Consider the difficulties Putin has in Ukraine, and then scale that up to US proportions.

The low standards of ICE and the nature of their operation would allow just about any organized actor to have a free hand in the US, if they chose to do so.

Covert operations? Probably. Asymmetrical warfare? Possibly.

Full-scale assault, with the objective to take and hold key administrative centers to force concessions? Hardly.