The U.S. Constitution states, "The President … shall have Power to grant Reprieves and Pardons for Offences against the United States, except in Cases of Impeachment." (U.S. Const., art. II, § 2, cl. 1.) This language gives the president broad pardoning power, with very few limitations. (Schick v. Reed, 419 U.S. 256 (1974).) Moreover, the pardon power is the president's alone—the president's decision to grant a pardon cannot be overturned by Congress or the courts.
The language in the Constitution highlights just two limits to the presidential pardon power. The president's authority extends only to offenses against the United States (federal crimes), meaning state crimes are beyond the president's control. And the president cannot circumvent Congress' power of impeachment. Beyond this, the president's power is restrained only within other constitutional limits. Let's explore these provisions further.
The President's power to pardon individuals extends only to federal—not state—crimes. Federal crimes generally involve federal or national issues, such as federal tax fraud, immigration violations, counterfeiting U.S. currency, and wire fraud. Most crimes are actually prosecuted at the state level, such as murder, sexual assault, and theft (as long as the crime doesn't cross state lines, at which points it becomes a federal crime). The president does not have the authority to pardon state offenses—that power is reserved for state governors. (Because state prosecutions are beyond the reach of presidential pardons, they can serve as an indirect check on the presidential pardon power.)
The pardon power extends only to offenses that have already been committed—those that are "known to the law." (Ex parte Garland, 71 U.S. 333, 380 (1866).) But, while future crimes are off-limits, the Supreme Court held that the president can exercise the pardon power at any time, even before legal proceedings start or the prosecutor knows of the crime. The crime just needs to have been committed.
Typically, the official document granting the pardon identifies the offense(s) being pardoned or, if charges haven't been filed, a time frame during which the alleged offense was committed. For instance, President Ford granted Richard Nixon a pardon "for all offenses against the United States which…Nixon…has committed or may have committed or taken part in during the period from January 20, 1969 through August 9, 1974." This pardon gave Nixon immunity from federal criminal charges associated with the Watergate scandal.
Nixon's pardon provides a great example of what many refer to as a "preemptive pardon." A preemptive pardon allows the president to grant pardons for offenses even before legal charges or proceedings are filed. Preemptive pardons essentially bypass the formal pardon process administered by the U.S. Department of Justice's Office of the Pardon Attorney. To qualify under the Pardon Attorney's regulations, a person must be convicted and sentenced, wait five years after release from incarceration or sentencing, complete all probation and parole, accept responsibility for the crime, and prove rehabilitative efforts.
But, if a president wants to make a point of pardoning someone before charging, trial, or sentencing takes place, the president is free to do so. In the Garland decision, the Supreme Court stated that the pardon power "may be exercised at any time after [the offense's] commission, either before legal proceedings are taken or during their pendency or after conviction and judgment." (71 U.S. 333, 380 (1866).) President Trump, for one, made frequent use of preemptive pardons, bypassing the Pardon Attorney's process and also rejecting its recommendations.
A presidential pardon—no matter how controversial—cannot be overturned. The Constitution gives the pardon power to the executive branch alone, not the legislative branch (Congress) or the judicial branch (federal courts, including the Supreme Court). Under the constitutional separation of powers, powers reserved to one branch cannot be infringed upon by another. In other words, just as the president cannot change a law, Congress cannot overturn a presidential pardon. (U.S. v. Klein, 80 U.S. 128 (1871).) Likewise, the Supreme Court's power to review is limited to constitutional violations (not politics).
No president to date has granted himself a self-pardon. While the issue has been broached (during the Nixon, Clinton, and Trump presidencies), no court has taken on the issue. Without legal precedent, it's unclear whether a self-pardon is constitutional. Even legal scholars' opinions on this issue land firmly in opposing camps.
Those who argue that the president has the power to self-pardon point to the language of the Constitution. The Constitution sets clear limits to the presidential pardon powers, stating the power extends only to federal offenses with the exception of impeachment. This camp points to the numerous Supreme Court rulings emphasizing virtually unfettered executive discretion to grant clemency, subject to only constitutional limits. Absent constitutional language to the contrary, it's argued a self-pardon is not off-limits.
On the flip side, others argue that a self-pardon contradicts the president's essential constitutional duty to faithfully execute the laws. Basically, a president cannot faithfully execute the laws and break them at the same time. And no one, not even the president, is above the law. This side points to a federal court decision highlighting that the president's broad pardon power does not live in a vacuum—rather, it lives within other constitutional rights and limitations. (Hoffa v. Saxbe, 378 F. Supp. 1221 (D.D.C. 1974).) A conclusion reached by the president's Office of Legal Counsel from 1974 also supports the conclusion that a self-pardon cannot stand, as it goes against the fundamental rule that no one can be a judge in their own case. (Presidential or Legis. Pardon of the President, 1 Op. O.L.C. Supp. 370 (1974).)