He allowed favoritism to taint his final decisions

In one of his last acts as president, Donald Trump again exercised his constitutional authority to "grant reprieves and pardons for offenses against the United States" in an irresponsible and offensive way — fortunately for the last time. The way he has used the pardon power to benefit cronies, political allies and the father of his son-in-law underlines just how expansive that power is — and why his successor must be pressed, including by Congress, to exercise it impartially.

As he has done in the past, Trump extended clemency to some deserving recipients, including nonviolent drug offenders. But there were also grants of clemency that favored people with ties to the president or the Republican Party.

Most egregiously, Trump pardoned his longtime adviser Stephen K. Bannon, who had been charged with fraud and money laundering in an alleged scheme to swindle supporters of Trump's border wall. The pardon for Bannon follows Trump's previous pardons of self-described "dirty trickster" Roger Stone, former Trump campaign chairman Paul Manafort and former national security adviser Michael Flynn, who pleaded guilty to lying to the FBI.

Trump also pardoned several politicians convicted of corruption charges, including former Republican Reps. Randy "Duke" Cunningham of Rancho Santa Fe, Rick Renzi of Arizona and Robin Hayes of North Carolina, adding to the list of disgraced former office holders whom Trump has favored. Also pardoned was major Republican fundraiser Elliott Broidy, who'd pleaded guilty to unregistered lobbying on behalf of foreign interests seeking to end a federal investigation into the 1MDB investment scandal.

The new grants of clemency were notable for what they didn't include: an arguably unconstitutional attempt by Trump to pardon himself. That may reflect less a sudden case of scruples than a fear that such an outrageous act would alienate senators who will sit as the jury in Trump's second impeachment trial.

Last July, in response to Trump's decision to commute Stone's sentence — the first of two times Trump used his power to benefit his longtime friend — House Speaker Nancy Pelosi proposed that Congress enact legislation to ensure that "no president can pardon or commute the sentence of an individual who is engaged in a coverup campaign to shield that president from criminal prosecution."

That idea raised constitutional issues, given the expansive authority the Constitution affords the president in the exercise of clemency. But later House Democrats proposed legislation that would sensibly require the Department of Justice and the White House to provide Congress with materials about "any self-serving presidential pardon or commutation in cases involving the president or his/her relatives, contempt of Congress, or obstruction of Congress." (The proposal also would have banned presidential self-pardons.)

Most presidents won't pervert the conduct of their office the way Trump did. But beginning with President Joe Biden, his successors must do better.