Good idea but written as nonsense. The plot depends on impossible scenarios and key characters doing really stupid things.
First big nonsense is that key people can challenge his right to be President. The fact is he was made President by the constitution and, as such, has full presidential authority. The assembled state governors, who force him to do a deal before they agree to nominate new senators or hold special elections to the House really have no choice in the matter. They are constitutionally obliged to do these things.
Then the effective head of the FBI acts in ways he never would, particularly in failing to indicate to the President his suspicions about the congressman who survived the massacre, even though it was clear that he might be made Vice President. The evidence against the congressman is compelling.
Disappointing and really not worth watching unless you like outlandish fantasy.