He didn't actually. Look carefully at your sources, and you'll see that nowhere does it state thatWell, of course, he already did use that option, but:
DOJ finds no evidence of voter fraud that would change 2020 election outcome
Rudy Giuliani dismisses attorney general’s statement, claiming there ‘hasn’t been any semblance of an investigation’www.independent.co.uk
A) Trump ordered an investigation
B) They actively investigated.
What Barr said was that they were following up on specific complaints, but that those complaints didn't turn up anything. That's not an investigation. That's reactionary.
So no, I don't think he has used that option, and I don't think he has the power to do that either. I imagine the states would rightly complain if federal authorities swarmed their departments, ransacked their offices, and started detaining people. My gut feeling is that there's a "states rights" legal issue with doing that.