Can special counsel Robert Mueller require President Trump to testify before a grand jury? It would be unprecedented, and his effort to do so could lead to a major constitutional confrontation.
The president could, of course, resist a grand jury subpoena by asserting his right under the Fifth Amendment not to be a witness against himself. However, for political reasons, he may not wish to do that. And he may not need to.
Another off-ramp for the president, which he may choose not to take, is to remove the special counsel. Mueller is an appointee of the Department of Justice, part of the executive branch. He is therefore a subordinate of the president. Trump might have to jump through some hoops to remove him—such as removing the deputy attorney general who selected Mueller—but he has the power to do so. If, that is, he’s willing to withstand the public outcry and demands for impeachment that would surely follow. Legislative measures, such as those already introduced in Congress, to shackle or impede the president’s power to remove the special counsel are almost surely unconstitutional. So the president could avoid a grand jury subpoena by removing the official who is threatening to obtain one. But this is another step with potentially grave political implications that he may not wish to risk.
The president is not “above the law”; there are many court decisions saying so. But the Constitution is part of the law, and it makes the president the sole repository of the executive power of the United States. He is therefore not just like any other citizen.