There's a pile of routes, and they're all over the place.

There's the individual state level "This effer voted twice" stuff.

There's the "Elections officials at precinct X are corrupt muthereffs"

There's "They're wildly at odds with state law in the way the ran things"

There's "They're at odds with Consitutional issues, like DUE PROCESS and another, term I'm blanking on"

*then There's military/intelligence/whoever maybe stepping up and screaming about "Foreign interference/this is war/etc/"

There's an American Thinker piece a couple days back that walks through this.

The Founders invisioned things like "Virginia is too fucked up to hold a vote this year - at all". The state choses their Electors. The state's various laws have whatever 'fallback positions' in them they want - and they're different.

There's too much weirdness to even attempt to parse. CA ruled "Newsom had no authority to send mail in ballots" ... well.. um ... Effing up CA changes everything, now doesn't it?

All we can do from the outside is observe anywhere that's still counting, press our reps to grow at least part of a spine.