Slightly more plausible than Bluetooth eatings where she had a full team of writers instantly coming up with her responses, all agreeing on it, and relating it to her with zero delay...
Eh, a lot of scam preachers have infamously done just that. What makes it unrealistic is the practical range for Bluetooth. And even if they figured that out, since they were not inside her ears canals they'd be effectively speakers which the mic would catch.
Even then, like, am I the only person who isn't against candidates having an earpiece and a team helping them? When do you ever think the POTUS is alone and making split-second decisions? They'll always have an advisor or some type of council around them.
This is supposed to be a presidential debate, not a president and team debate.
Also at the end of the day it's the president that makes the decisions, not the team. You're supposed to evaluate them, in part, on their decision making capability.
I'd support it for fact checking alone. Give them a researcher in their ear who can search the internet for reliable references. It would discourage bullshitting on both sides, and someone like Trump would be instantly shut down.
Instead of an invisible fact-checking team, give them each a laptop (or phone) so they can do their own fact checks, and make the screens visible so we can see what sources they use.
As improbable as the latter sounds, the former (supernatural powers) I consider to be impossible. And when you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth.
.. which in this case is just that Harris is competent and the other guy is not. No supernatural witchcraft or impossible earbuds required.