They would never attempt it from the outside while we're strong. Injecting these conspiracy theories and other societal "inflammation-inducing" pathogens are giving rise to a cancer that's slowly eating our society from the inside out. Republicans are willing participants in hobbling our collective immune system because that same weakness helps their dystopian message get through to the US electorate, scaring them enough to get more Rs elected (as though they can fix any of the problems they reference, or even care about them), then install more brain-addled, dominionist judges and cut taxes for billionaires and corporations, and here we are.
Plus - doing this all via the internet and social media spreads the message at the speed of light, and is essentially free. Is certainly free compared to the costs associated with attacking the US with bombs and troops. Nice game, huh?
From whence shall we expect the approach of danger? Shall some trans-Atlantic military giant step the earth and crush us at a blow? Never. All the armies of Europe and Asia...could not by force take a drink from the Ohio River or make a track on the Blue Ridge in the trial of a thousand years. No, if destruction be our lot we must ourselves be its author and finisher. As a nation of free men we will live forever or die by suicide.
― Abraham Lincoln