I don't think you have much to worry about in the US. From my experience, those who call themselves "Marxist" have a hard time organizing a barbecue, let alone a revolution. They are mostly revolutionary LARPers. I think the internet and media sometimes magnify the size and power of these groups and it warps with our perception of reality. The largest Leninist group in the US is the PSL and they're a joke. A bunch of weirdos with no friends but the ones they found online