President Donald Trump's long-serving personal lawyer, Michael Cohen, pleaded guilty to twin federal election law offences directly implicating the President. Mr Cohen's statements set the foundation for the United States Attorney for the Southern District of New York to subpoena Mr Trump to testify about $280,000 paid to a adult film star (Stormy Daniels) and a Playboy model (Karen McDougal) during his 2016 campaign for their silence about his decade-old affairs with each to influence the outcome of the election. The disclosures could have alienated his religious right-wing supporters.

Mr Trump is likely to resist the subpoena. That would force a challenge in the United States Supreme Court as to whether a sitting president is accountable to the criminal law, as are all other officers of the United States, including members of Congress and justices of the Supreme Court. The controlling precedents are against President Trump. In United States v Nixon, the Supreme Court unanimously compelled President Richard Nixon to surrender presidential tapes and documents for use in a criminal trial against his top assistants. None of Mr Nixon's four Supreme Court appointees voted in his favour. In Clinton v Jones, the Court held that President Bill Clinton could be compelled to testify in a civil suit bright by Paula Jones alleging sexual harassment. Neither of Mr Clinton's two appointees voted in his favour. Mr Trump is similarly unlikely to win the votes of Justice Neil Gorsuch, whom he appointed, or Brett Kavanaugh, whose nomination will soon be confirmed. They would strain to avoid an appearance of bowing to their benefactor as did the Nixon and Clinton justices.

An adverse ruling by the Supreme Court would end the Trump presidency. If he defied the Supreme Court's order, he would be immediately be impeached by the House for subverting the Constitution's separation of powers, convicted in the Senate by a two-thirds majority, and removed from office. (Attempts to subvert the Constitution are made impeachable offences, ie, high crimes and misdemeanours, under Article II, section 4). The Supreme Court remains the nation's most venerated and untarnished civil institution. Any attack on a decision joined by Trump's own appointees would ring hollow.

President Trump would be equally doomed if he agreed to give testimony under oath. In his mental universe, he does not distinguish between truth and falsehood. Perjury would be inescapable. He has already lied repeatedly about pay-offs to the two women. His foremost lawyer and spokesman, Rudy Giuliani, has insisted "truth isn't truth" in explaining why Trump's testimony would inexorably prove perjurious. Perjury is an impeachable offence, and occasioned President Clinton's impeachment by the House of Representatives.