(CNN)The assertion of Donald Trump's lawyer that a president can never be guilty of obstructing justice because he is the country's top law enforcement officer recalls Richard Nixon's remark that "when the president does it, that means it is not illegal," and intensifies debate over whether a sitting president can be indicted.
Trump lawyer says a president can't 'obstruct justice.' Can that be true?
Whether a president can be criminally charged -- for any offense -- has never been tested in the courts. But presidents have been subject to obstruction-of-justice charges in impeachment proceedings. And there is no question that a president can be removed for, as the US Constitution dictates, any "high crimes and misdemeanors."
Unlike a criminal case heard by a judge or jury, impeachment is a political process that comes down to votes: a majority in the US House of Representatives to impeach and a two-thirds vote of the US Senate to convict. Yet both sets of proceedings can follow the kind of special counsel investigation now underway. Comparisons to the Nixon scandal have been rife recent months. In Watergate, Nixon was not criminally charged but was named as an unindicted co-conspirator and pressured to resign with impeachment charges looming.
The deal between special counsel Robert Mueller and Trump's former national security adviser Michael Flynn ramped up controversy over whether Trump had known Flynn had lied to the FBI, as Flynn pleaded guilty to last Friday, and perhaps tried to interfere with the federal investigation of Flynn. Former FBI Director James Comey, who oversaw the Department of Justice probe related to Russia interference in the 2016 election before being fired by Trump in May, said Trump had asked him to stop pursuing Flynn.
A Trump tweet on December 2, 2017, suggested Trump knew before that request to Comey that Flynn had lied when he was fired. If so, that could increase the possibility that Trump was trying to impede Comey's pursuit of Flynn's potentially criminal behavior.
With that storm brewing, Trump's personal lawyer John Dowd told Axios that "the President cannot obstruct justice because he is the chief law enforcement officer (under the Constitution's Article II) and has every right to express his view of any case."
But the Constitution is silent on the issue. And since Nixon and Watergate, lawyers inside and outside the executive branch have debated whether a president may be criminally prosecuted.
In the early 1970s, Nixon was involved in the cover-up of a June 1972 break-in at the Democratic Party headquarters in the Watergate building. His denials of any wrongdoing dramatically undercut when White House tapes of related conversations were discovered. Nixon resigned in August 1974, shortly after the US Supreme Court ruled he had to turn over the tapes to a special prosecutor.
Later in 1977, in a series of interviews with journalist David Frost, he remarked that when "the president does it, that means it is not illegal." The comment, addressing national security and broader presidential power, has been one of the most startling and enduring from those televised interviews.
During Watergate, the Department of Justice's Office of Legal Counsel concluded that criminal prosecution of a sitting president would undermine the executive's duty to carry out his constitutional duties. In 2000, the office reiterated that 1973 position that the Constitution forbids the indictment or criminal prosecution of a sitting president.
Still, lawyers then and now say the real answer would rest with the courts, and some lawyers argue that since the Constitution does not address the question, the US Supreme Court could ultimately find that the president was not above prosecution.
Nixon's threatened impeachment, as well as President Bill Clinton's actual impeachment in 1998, both began with reports from special prosecutors in roles such as Mueller's. Obstruction-of-justice charges were leveled in both cases.
In the Clinton ordeal, the Republican-dominated House of Representatives passed two articles of impeachment in December 1998 related to obstruction of justice and perjury. The Senate acquitted Clinton in February 1999 after the chamber fell short of the two-thirds majority required for conviction. The only other US president to be impeached, Andrew Johnson in 1868, was similarly not convicted by the Senate.
So far Mueller has charged Flynn and three other individuals from the Trump campaign with crimes -- former campaign chairman Paul Manafort and his deputy on the campaign Rick Gates were indicted (both have pleaded not guilty), and a plea deal was reached with former adviser George Papadopoulos.
It is not known whether Mueller is building a case against the president and whether he would be inclined to put it before a criminal court rather than the House of Representatives.
Obstruction of justice, which Trump lawyer Dowd mentioned, is a federal offense that arises when someone tries to "influence, obstruct, or impede" the "due administration of justice." A key question is whether the President or any defendant acted with a corrupt intent.
Much of the criticism of Trump's actions related to the Russia probe go back to when Trump asked Comey to drop the Flynn investigation and then fired him.
Whether that or any of the President's other actions would offer sufficient grounds for an obstruction-of-justice conviction could rest with a court, or it may turn out, only with the two chambers of Congress.