After Republicans next win control of the presidency and both houses of Congress, will they maintain control for the following ten years?

In other words, after the Republican party next gains control of the executive and legislative branches, will they win the following two midterms and elections?

The possibility of Republicans putting to end to democracy in America is being increasingly discussed as midterm elections near. I wanted to put a number on that possibility. I tried to choose a set of resolution criteria which would be as objective as possible.