Socialism's linchpin is centralizing the economy under political direction; its need for a central plan implies that the political system would be centralized too. The more centralized the State, the fewer centres of power there are. The fewer centres of power, the fewer centres a foreign conqueror needs to hit in order to take over the country.
Thus, ceteris paribus, the more socialistic a State, the more vulnerable it is to foreign conquest.
Consquently, socialists (whose aim is to stay in charge) will quickly figure out that they'd better make sure the ceteris is no longer paribus. To compensate for socialism's military vulnerability, they have to boost the military. Instead of swords being beaten into plowshares, plowshares get beaten into swords. That's one of the reasons why socialist states end up being First-World militaries on top of Third-World economies.
Interestingly, there's a side consequence: under socialism, a career in the military becomes a cushy slot. Military minds will figure the same vulnerability out quickly, which gives them real leverage over the commissars. I wouldn't be surprised to learn that the political-officer slots in the military were the Communist Party's equivalent of the Russian Front.
It’s interesting also that socialism depends on the people being dependent.
If the people are independent go-getter do-it-yourself types, then the theory of socialism fails, and alot of politicians (who have based their careers on “DOING SOMETHING”) lose their jobs.
We need unemployment, we need Obamacare, we need food stamps, it generates hundreds of thousands of paper-pushing jobs...
/sarcasm
Seems the goal wouldn’t be to take over, but just to break the leadership. Sufficient disruption would get US out of the way for other megalomaniacs to get on with their goals. Flaw in the plan is our military would remain intact, and have motivation (and lack of resistance) to carry out lots of well-laid plans.
As described, the disruption could be effective but brief. Some Congresscritter would be recognized as “next in line”, would assume temporary role of POTUS with military backing, appoint occupants of all empty seats, initiate elections (which are operated by the states), and within a few months be back to normal. In the meantime, the entire bureaucratic structure would remain intact and functional.
Upshot: evening news would be buzzing for a while, and a few petty fights would break out, but we’d be back up & running in short order with little change save for some names - and a very bad attitude.