Former FBI chief Robert Mueller, the special counsel investigating if Russia colluded in last year's bitter election campaign. What happens if he concludes T

The legal debate surrounding Special Counsel Robert Mueller’s ongoing investigation continues.

US attorney general under George W Bush, Michael Mukasey, argues in the pages of the Wall Street Journal that, knowing what we know, there is no legal case against Trump, and asks: if there was, what would Mueller even be able to do with it?

“What if—for some reason not apparent to the public now—Mr. Mueller were to conclude that the president did act ‘corruptly’? Could he initiate a criminal prosecution? The Office of Legal Counsel at the Justice Department, which sets policy for the department and other agencies of government, has already opined more than once—starting in 1973, during Watergate—that the answer is no. It would offend the Constitution for the executive branch to prosecute its head.

What else might Mr. Mueller do? Some have suggested that if he finds criminal activity occurred he could report his findings to the House so as to trigger an impeachment proceeding, as Independent Counsel Kenneth Starr did in 1998. But the law under which Mr. Starr was appointed has lapsed, and the regulations governing the special counsel provide for only two kinds of reports—either to Justice Department leadership when some urgent event occurs during the investigation, or to the attorney general to explain the decision to prosecute or not. Reports of either type are to be treated as confidential.

Mr. Mueller could simply take the bit in his teeth and write a public report on his own authority, or write a confidential report and leak it to the press. If he did either, he would be following Mr. Comey’s lawless example.

Or if, as appears from what we know now, there is no crime here, Mr. Mueller, notwithstanding his more than a dozen lawyers and unlimited budget, could live up to his advance billing for integrity and propriety and resist the urge to grab a headline—not necessarily his own urge but that of some he has hired.

Hold fast. It may be a rough ride.”