We have never cancelled an election in this country, not even during the Civil War, or WW2. So there is absolutely NO acceptable rationalization for him to stop elections.
Elections are managed by the states, so even if he demands they stop, they don't have to obey him. Blue states probably won't, and even Red states won't want to obey him. They have political ambitions, too, and they have a lot more races than just Congress. They have state legislators, mayors, county commissioners, sheriffs, etc. Stopping elections messes up the entire system , top to bottom. It's literally impossible to stop elections, the entire system will crash.
And then there's the reaction from the Citizens. Without elections, we no longer have a Democracy, and if we don't have a Democracy, then we are not obligated to follow any laws, nor respect law enforcement of any kind. Violence will follow.