The least the nation should expect from a president is respect for our system of justice and the constitutional structure of separated powers within which it operates.

Since he launched his campaign for president, Donald Trump has exhibited stunning ignorance of and utter disrespect for the rule of law. Through his statements and actions, the president has trampled a field of long-respected constitutional norms essential to the survival of our justice system.

Here are a few:

1. The president must not politicize the administration of justice by commenting on the guilt, innocence, or desired punishment of individuals charged with crimes.

The Constitution obliges the president to see that the laws are faithfully executed, making him the nominal head of federal law enforcement, but his functional role has been defined by constitutionally driven norms that protect the rule of law. We recognize that the president can set law enforcement policies, but that he may not dictate who will be a subject of criminal prosecution. So the president can properly say that we need to crack down on the crimes of money laundering and income tax evasion, but he should not declare that Paul Manafort should be prosecuted and deserves the death penalty. Indeed, presidents have learned that it is not only inappropriate, but often counterproductive to use their bully pulpits to prejudge a suspect’s guilt or demand a harsh punishment. Such politically tempting outbursts delegitimize the careful process by which we determine guilt, prejudice jury pools and complicate judges’ sentences.

Trump repeatedly has denounced individuals charged with crimes and demanded harsh punishment. Last week, he called the suspect who allegedly drove a rented truck on a bicycle path in New York, killing eight people, an “animal” who should get the death penalty. The statement greatly complicates the prosecutors’ task. Trump’s intemperate tongue has reached into the military justice system. On Friday, news broke that a military judge had limited Sgt. Bowe Bergdahl’s punishment to a demotion and dishonorable discharge. As both candidate and president, Trump called for Bergdahl’s execution and called him a “dirty rotten traitor.” The judge who issued the sentence said that he would consider Trump’s statements as mitigating evidence. Trump called the verdict a “disgrace.” On appeal, defense lawyers will offer Trump’s statements as an attempt by the commander-in-chief to pressure military judges.

2. Presidents do not demand prosecution of their political opponents.

Use of criminal prosecutions to target political enemies is a direct threat to the rule of law. Authoritarian rulers do it. Leaders of vibrant democracies do not.

Throughout our history, presidents have understood the danger in demanding prosecution of defeated political opponents for crimes committed in the course of a political contest. The pursuit of criminal charges against political adversaries allows a leader to entrench himself in office and to deter democratic challengers. It erases the line between politics and law.

Trump, however, has not hesitated to demand that the FBI investigate and the Department of Justice prosecute Hillary Clinton for non-meritorious matters including her involvement in a 2010 uranium deal, her use of a private email server, and her destruction of emails. He has encouraged investigations of Clinton and the Democratic Party for involvement in funding the Steele dossier and for the Clinton campaign’s alleged cheating in the Democratic primary. Trump’s chief of staff, John Kelly, further diminished himself by calling for a prosecutor to go after Clinton.

Trump’s demands have grown more frantic as the Russia investigation has closed in. His frustration boiled over in an interview on the eve of his trip to Asia, in which he confessed that he understood that he was not supposed to interfere in the prosecution decisions of the Department of Justice, but ominously stated he was greatly frustrated by the restriction.

3. The president must respect the independence of the attorney general and the Department of Justice.

Nothing in the Constitution explicitly commands the independence of the attorney general and Department of Justice from the president. Yet, adherence to the rule of law demands a degree of independence to insulate law enforcement from politics. Over the years – particularly since Watergate – a series of norms have developed that limit communication between the White House and the Department of Justice to prevent the president and his assistants from influencing law enforcement decisions. Some communication is essential. The president must be able to discuss policy priorities with the Department and the Department must be able to keep the White House informed of significant developments. In addition, the White House should seek and follow the Department’s legal advice. But regarding criminal investigations and prosecutions, a wall with strictly controlled gates has grown up between the White House and the Justice Department. Trump has breached that wall repeatedly.

Trump’s demands for loyalty from FBI Director Comey and his continuing dissatisfaction with Attorney General Sessions reflect Trump’s view that they should be personally accountable to him. He expected to be able to steer the FBI away from investigating Michael Flynn. He remains upset that Sessions recused himself from the Russia investigation, rather than remaining engaged to protect Trump.

Similarly, Trump reportedly has personally interviewed candidates for U.S. Attorney positions in Manhattan and Washington, D.C. It is rare for a president to interview U.S. Attorney candidates and it is particularly worrisome for him to interview the candidates most likely to investigate his conduct.

Past administrations have been caught attempting to politicize the Justice Department through personnel decisions. Notably, the George W. Bush administration suffered a scandal over its firing of U.S. Attorneys who refused to allow politics to dictate criminal prosecutions. The Justice Department’s Inspector General also found that the Bush administration had politicized the hiring of career attorneys. Trump will be greatly tempted to do it again.

4. The president must respect the independence and integrity of the judiciary.

Trump is a bully. Only Melania seems not to have noticed. Through his personal attacks and juvenile name-calling, he attempts to bully his way to desired goals, diminish the status of others to bolster his fragile ego, and undermine institutions, including the press and the courts. He has matched his assaults on the FBI and Justice Department with recurring criticism of courts and individual judges. Trump lashed out during the campaign at Judge Gonzalo Curiel, claiming that Curiel’s Mexican heritage would prevent him from ruling fairly on allegations of fraud regarding Trump University. As President, he attacked all of the judges who struck portions of his travel ban, labeling one a “so-called” judge. He denounced the district court judge in San Francisco who blocked his executive order on sanctuary cities. Disagreeing with a judicial ruling on the legal merits is fair game, but Trump’s very personal attacks are intended to delegitimize judges and the courts on which they serve. He criticizes them for getting in his way, heedless of legal argument. He thereby disputes their role as an independent branch of government with a constitutional mandate to check the president when he acts unlawfully. He, of course, uses his criticism to fire up his supporters. Consistent with his bullying personality, he likely thinks that he can influence judicial behavior with his criticism.

Trump either does not understand or simply rejects the role of an independent judiciary. He appears to view the entire justice system, including the FBI, Justice Department and the courts as subordinates who are expected to implement his wishes and protect him from attack. Trump’s organized-crime view of government should make us all wary of accepting the legitimacy of his judicial nominees. Too often, his nominees have been unqualified and unlikely defenders of the rule of law against a bully executive. Supporters of the rule of law and the safeguards of our constitutional structure must resist the nominees of a president who thinks our justice system is “a joke” and “a laughingstock.”

Bill Yeomans is the Senior Justice Fellow at Alliance for Justice. He currently serves as Lecturer in Law at Columbia Law School, and previously taught constitutional law, civil rights, and legislation at American University Washington College of Law. He also served for 26 years in the Department of Justice, where he litigated cases involving voting rights and discrimination in employment, housing, and education, and prosecuted police officers and racially motivated violent offenders before assuming a series of management positions, including acting Assistant Attorney General. For three years, Bill served as Sen. Edward M. Kennedy’s chief counsel on the Senate Judiciary Committee, and has also held positions at AFJ and the American Constitution Society.