That’s not a power the President has. The President cannot postpone them and they aren’t included as an emergency power. So he can’t call an emergency and suspend elections. And yes, we’ve got precedent from the Civil War that elections can’t be suspended when we’re at war with ourselves.

States can remove themselves, but that just means fewer folks arrive in Congress. Unless the President forcefully dissolves Congress, which would require a lot of the military being okay with murdering elected officials, only Congress can have a say on the law.

The President can indicate that they’re rigged and what have you. But he only gets away with it, if Congress or the Courts or both goes along with it. That’s the only means that doesn’t require murdering people. All the other methods will require force. Including the “it’s all rigged”. California can have their midterm election, certify it, and send their members of Congress to DC. If Trump stops them, they can sue to be rightfully seated. That requires the Courts to go along with it. If the Courts allow them in, but the Speaker won’t acknowledge them or grant them a vote, that’s Congress going along with it.

The only way the Executive alone prevents a member of Congress from taking their duly elected seat is shooting them in the head. That’s it, that’s the only means. All the other methods require some other ⅓ of our Government being cool with the heist.