https://www.weeklystandard.com/theodore-b-olson/mueller-v-trump
Theodore B. Olson
Theodore B. Olson is a former solicitor general of the United States.
The importance of all this to the president is that it is unlikely that he can be forced to give grand jury testimony simply to satisfy Mueller’s curiosity and submit to a potential perjury trap. He could, in short, put Mueller to his proof—make Mueller show that the president’s testimony was necessary to prosecute someone else. And that such evidence could not be obtained elsewhere. That is a high bar, indeed, and one that at this point Mueller has not shown he would be able to surmount.