Can’t say I’m particularly worried about any infiltration plans. There’s growing evidence that the groups who most want to help Trump to remain in office somehow are, well, a bit shit at this conspiratorial stuff.
The same goes for any type of organized plan. The real threat is from some lone nutcase (who might be in the National Guard, hence the vetting) deciding they have nothing to lose, and wanting to go out in a blaze of glory. Presumably, there’s no chance of them getting within five miles of Biden.
Longer term, there greatest danger could come from foreign agents recruiting the Trump cultists as useful idiots and cannon fodder and providing the organizing skills they currently lack.