Suppose he loses the election but good ol' Johnson deems the whole election invalid and throws it to the house...how plausible is this scenario? I recall they wanted to test the waters on that, what is their mechanism?
IMO there's not a lot of point in us discussing the likelihood of specific scenarios. Coups rely on a fair bit of luck as well as the ability to manage situations that weren't anticipated, such as someone who was expected to toe the line being pushed by the coup plotters and ends up not doing so, or vice versa.
IMO the state either needs to put itself in the position whereby it can anticipate the moves of likely plotters and shut things down preferably by peaceful/lawful means and have the law ready to back up the guilty parties' permanent removal from office and subsequent imprisonment, or it needs to be immediately ready to put down any plots with deadly force.
Either approach involves the state getting its hands dirty, for example the corrupt judges on the supreme court need to be coerced into doing their jobs properly (e.g. blackmail), monitoring comms in a not-entirely-legal way, or for example any politician attempting to live tweet security sensitive situation in a coup scenario gets a bullet in their head.
Freedom isn't free, and the GQP has tried to take it using multiple tactics. They have no interest in playing by the rules. The question is, how far is either side willing to go. Would the last coup have been successful if there was an armed unit in the employ of the GQP, for example having Mike Pence with a gun to his head. A competent administration should plan for all conceivable contingencies.