Nukes. Yes, I really do think they are that stupid. They have a childish mentality about Taiwan, and if they cant have it, then no one should.
Also remember, they seem pretty good at hacking and taking shit down, not to mention a shit ton of collaborators over here. They have plans, and I very much doubt they are conventional, Think about the Betrayal scene in Dune and you've got a pretty good idea of how I think this is going to start.
Something I've wondered... the West Coast cities are getting increasingly woke and insane to the point of having many elected officials who vocally support communism. The ports are controlled by woke unions and the woke local government. Many of these groups vocally support China and then there's the matter of the large populations of Chinese in those areas.
What if the local governments in, say, Portland, Seattle and San Francisco conspired to have thousands of PLA troopers brought over on container ships to occupy each city? The police forces in the cities have been cut to the bone and wouldn't stand a chance against such an invading force. Sneaking them in through the ports would allow them to take over without drawing attention from the military. The invasion could take place over a night where they roll all the troops along with tanks, artillery pieces and anti-air batteries out of shipping vessels and quickly take over the cities; they would have plenty of time to plan all this out.
The PLA could effectively make each city a massive military base with the residents used as human shields. It would be impossible to shell or bombard them without killing hundreds of US civilians. The Chinese troops wouldn't be able to take much ground beyond the cities because they would be blasted if they got too far from their human shields, but they could make life hell for the US in the mean time. They could hold a significant chunk of the country's shipping capacity hostage and demand all kinds of concessions.
The city governments would function as Vichy leaders with promises that they'll get to lead the new "socialist republics" that have been carved out of the US once the revolution is complete. China would claim they're on a mission to "liberate the oppressed peoples of the United States white supremacist system" and they'd have a bunch of city council members and union leaders from the cities backing them up.
After the invasions happened the Navy could cut off China's access to the cities, but the PLA could use the millions of hostages to their advantage by threatening to withhold food and starve them if the supply lines aren't left open. They could wall the cities like Berlin and not permit any supplies to come in from the US., saying if the people in those cities are to be permitted food it must come from China along with more PLA troops and materiel.
Taking those cities would also put them in control of a huge amount of technology infrastructure. Imagine if Facebook, Twitter, Amazon and every other tech company HQed in those places fell under PLA control? Even if they couldn't take over Amazon per se, shutting down its HQ would cripple its ability to deliver things until they could get an alternate system set up to run all their fulfillment centers. Think what it would do the the country if Amazon suddenly stopped operating.
Biden in the meantime would wet his diaper and call a lid for the day.