Washington: US President Donald Trump's pardon of former Arizona sheriff and civil rights abuser Joe Arpaio raises the question of whether the President may act with impunity to pardon individuals caught up in special counsel Robert Mueller's investigation of the Trump campaign's dealings with Russia.

Based on my experience studying the pardon power during the Watergate investigation, I believe the answer is no.

Almost certainly, a presidential decision to preemptively pardon any of those caught up in Mueller's investigation, whether former campaign chairman Paul Manafort, former national security adviser Michael Flynn or Donald Trump jnr, would be effective and would spare those pardoned from prosecution, at least on the federal level.

So Trump may be tempted to use this mechanism to extricate himself from what he calls derisively "the Russia thing".

But issuing pardons to his own friends, associates and relatives could be a perilous path for Trump, creating additional exposure on two levels, criminal and political - both flowing from an important proposition that is often overlooked in the debate over presidential power.

The US legal system provides mechanisms for probing the intent and motives behind the exercise of power. The President may have the power to grant effective pardons in the Russia investigation, but both Congress and the federal prosecutor are entitled to determine whether the exercise of that power violates constitutional and statutory norms.

The most obvious constraint is the authority of the House of Representatives to determine whether an effort to squelch an investigation into criminal misconduct by people close to the President constitutes an impeachable offence. The core concept behind "high crimes and misdemeanours" is abuse of political power in violation of the best interests of the nation.

Thus, it would not be necessary for the House to conclude that the decision to issue pardons constituted a conventional "crime". All that would be required would be to find that the motive for pardons was to protect the President's personal interests and political future by cutting off the investigation into the misdeeds of those around him.

While impeachment remains an unlikely political prospect at the moment, so it was during Watergate - until the "Saturday Night Massacre" dramatically changed the political landscape. A decision by Trump to pardon his close friends and associates for any complicity in colluding with a hostile foreign power could easily trigger a similar firestorm, with comparable political consequences.

But Trump should not ignore the potential criminal pitfalls of exercising his pardon power in this context. As with any other presidential power, the power to pardon is constrained by the ordinary requirements of federal law applicable to all public officials. For example, if representatives of a pardon-seeker arrived in the Oval Office with a bundle of cash that the president accepted in return for a pardon, there is little doubt that the president would be guilty of the crime of bribery.

More apt than bribery in the current context is the array of federal statutes that make it a crime to "obstruct justice". Those statutes turn on the motive behind a person's action, even if the person otherwise has the power to take the action. For example, under Section 1503 of the federal criminal code, any person who "corruptly . . . influences, obstructs, or impedes, or endeavours to influence, obstruct, or impede, the due administration of justice" commits a felony. If Trump were to pardon any of the figures in the current Russia investigation, his action would certainly impede or obstruct the due administration of justice, as the courts have broadly construed that standard.

It would not be difficult to imagine Mueller making the case that the motive behind such interference was "corrupt". As the Founding Fathers made plain, the purpose behind the pardon power is to extend mercy to those who have offended and have demonstrated remorse. Using the pardon power to protect the president's own interests against embarrassment or exposure is not legitimate. Rather, a crassly self-interested exercise of presidential power to impede the due administration of justice is the very antithesis of the president's most solemn oath - "to take care that the laws be faithfully executed".

And that is why Trump should take care - to make sure that wielding his pardon power, however tempting, does not blow up in his face. An attempt to use pardons to defend his presidency may end up imperilling it instead.

Lacovara, a former US deputy solicitor general in the Justice Department, served as counsel to Watergate special prosecutors Archibald Cox and Leon Jaworski.

Washington Post