Mexican cartel, secessionists, or Islamists in the West

Those groups are already armed. Islamists have no reason to revolt because they're the establishment's beloved pet. The cartels are heavily armed and make serious money and are quite satisfied with the status quo.

Secessionists have weapons but have no leadership, ideology, or balls. The Russians should send agents to organize them in secret though such an act would invite massive retaliation from the American regime. Russia though strong is nowhere near the level of the US even as it decays.