We would have a mutual defense pact with four huge armies coordinating the defense of N.A. This is not hard.
But it's a lot harder. Let's say the independent state of Californicatia invited the ChiComs to land troops on their territory. We'd be fighting two nation-states at once, including one bordering us, including troops and agents who look and speak just like real Americans.
Do I think it would be easy to crush the internal enemies we have now in several states? No. Do I think it would be easy for them to wage a civil war against Normal America? "No" x 10, since those (current) states for the most part don't even control the countryside within their own borders.
Either way, the patriot states would have allies within the snowflake territories. The problem is the vastly increased cost of not controlling thousands of miles of your own coastline when foreign entities are bringing in heavy weapons and foreign troops.