President Trump speaks Friday at the 2018 Ohio Republican Party State Dinner, in Columbus, Ohio. (AP)
Bradley D. Hays is an associate professor of political science at Union College. His scholarship is on constitutional politics, history and development.

Paul Manafort: convicted. Michael Cohen: pleaded guilty. David Pecker and Allen Weisselberg: granted immunity. Suffice to say, it hasn’t been a good week for President Trump. As his close associates land in legal jeopardy, speculation has turned to the presidential pardon as possibly the only means Trump may have to save his presidency.

Legal commentators typically note that, while such pardons would be extraordinary, Trump has the power to issue them. A few commentators have even speculated that Trump could pardon himself. These assessments are based on constitutional law and the text of the Constitution.

But the pardoning power has operated, by and large, adjacent to constitutional law, in a realm of tradition and precedent that provides far more brakes on presidents than the law does. Put another way: presidents are constrained by the way their predecessors have used the pardon power. Ignore these constraints and political consequences will follow, up to and including the Constitution’s solution for presidential overreach: impeachment.

Let’s start with the easy case of a presidential self-pardon. No president has ever tried to pardon himself. And while that owes primarily to a lack of criminality among presidents — there have by and large not been crimes to pardon — there has also long been a presumption that such action would not be acceptable.

As early as 1798, Supreme Court Justice Samuel Chase argued that “a law that makes a man a judge in his own cause … [goes] against all reason and justice … To maintain that our federal or state legislature possesses such a powers if it had not been expressly restrained would, in my opinion, be a political heresy altogether inadmissible in our free republican governments.”

By 1952, such a principle was axiomatic enough to be acknowledged by a president. Almost as an aside in a speech to cadets at West Point, President Harry Truman noted the limits on his authority, saying, “The President has power to pardon anybody for anything but impeachment. Of course, he couldn’t pardon himself.” Truman returned to this theme just four days later, in Annapolis, noting again that a president cannot pardon himself because “that would be himself.”

Truman was not arguing that a president cannot pardon himself as a matter of textual, constitutional interpretation. He wasn’t saying that there was a written limit on his power — but he was acknowledging that this precedent had become part of American constitutionalism, and violating it would provoke swift political consequences.

Nothing has changed subsequently to erode or upend this premise. Even Richard Nixon never pardoned himself. It took Gerald Ford to do it after Nixon left office with the threat of prosecution looming.

Turning to a presidential pardon of Trump associates who violated federal law: Trump has the legal power to issue such a pardon. But any pardon he issued would be necessarily constrained by how past presidents have used their pardoning power. Clemency, after all, depends heavily on past exercise for its present legitimacy.

Of course, presidents are not limited to using the pardon power as their predecessors have. Sometimes new circumstances demand a new sort of pardon. But presidential innovators have been careful to reshape the pardoning power in ways that made use of the frameworks and ideas created by past pardons.

George Washington set a crucial standard that has been interpreted and advanced by centuries of presidents when he cited the need to promote national unity in his pardon of the participants in the Whiskey Rebellion. James Buchanan, for one, harked back to Washington by offering a pardon to quell a Mormon rebellion and promote national unity. But Buchanan also sought to protect local popular sovereignty, which was at the root of safeguarding not just polygamy in Utah but also slavery in the south. Wielding Washington’s framework was actually part of his failure to sufficiently address the slavery question that ended up prompting the Civil War.

More than a century later, Ford also considered the national good when he pardoned Nixon, citing both the need for the nation to heal and Nixon’s fallen legacy as sufficient punishment. Ford was forced to reference the latter because Nixon himself had blended notions of individual merit with clemency such that a pardon would only be issued for someone who warranted it by having accepted the appropriate punishment. Ford’s move provoked political outrage at the time, but over the years, Americans came to realize that it was a statesmanlike act that saved the country from further trauma.

Like Nixon, Ronald Reagan emphasized merit in pardoning former FBI officials Mark Felt and Edward Miller, each convicted of violating constitutional rights of American citizens, because their service to national security merited it.

Barack Obama, in turn, demonstrated how much past precedent constrains the pardon power. He sought to address racial inequities in drug sentencing through the pardoning power. Indeed, he used that authority to commute an unprecedented number of sentences.

Yet the sweeping changes that many desired never occurred because — thanks in part to the thinking of Nixon and Reagan — Obama needed to tie clemency to merit and this limited the scope of eligibility for the pardons. Obama would have faced political blowback if he had pardoned people whose individual records did not seem to warrant clemency. The uproar would have undercut the legitimacy of his action and possibly set back the broader cause of rectifying sentencing disparities. These political concerns placed a real limit on this theoretically unlimited power.

In each of these pardons, the president pursued a different political objective — but each had important links to past pardons that were necessary for their legitimacy.

This takes us back to President Trump and his current legal difficulties. Trump has proven willing, almost gleefully so, to break with precedent before. But pardoning his associates would take him into uncharted territory.

Many have pointed to his pardon of Joe Arpaio as revealing his willingness to use the pardon for partisan purposes. But by citing Obama’s pardon of Oscar Lopez Rivera, a militant for Puerto Rican independence, Trump framed the Arpaio pardon as responsive to Obama’s own racialized use of clemency.

In other words, while Trump regularly challenges the status quo, when it comes to the pardon, he has faced the typical presidential requirement of reconciling the past with his present objectives.

And there would be no such precedents for him to cite to justify a pardon of Manafort or any other associates who may become ensnared in legal problems. Thus, from the perspective of presidential history and institutional practice, breaking fully with the past by pardoning his associates or himself would truly be institutional heresy. And in this area, such a break should trigger the only other mechanism designed to protect what is fundamental in our very real and vital constitutional tradition: impeachment.