The Compulsory Process Clause of the Sixth Amendment to the United States Constitution allows defendants in criminal cases to secure witnesses in their favor through the issuance of a court-ordered subpoena. The Clause is generally read as allowing defendants to present their own case at trial, though several specific limitations have been announced by the Supreme Court of the United States since this rule began.
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History
The Compulsory Process Clause was part of the Sixth Amendment, which was ratified in 1791. Between ratification and the Fourteenth Amendment, there were very limited instances in which a court dealt with compulsory process. One important example is the trial of Vice PresidentAaron Burr, where Burr tried to subpoena documents from the President in order to sustain his defense. Though the case was heard in Federal Circuit Court the presiding judge was Chief Justice John Marshall who ordered the papers be issued, invoking the Sixth Amendment. After the passage of the Fourteenth Amendment in 1868, the Supreme Court dealt with a series of cases regarding the guarantees offered by the Due Process Clause. The first case to evaluate the procedural trial rights of defendants in terms of the Due Process Clause was the 1897 decision in Hovey v. Elliot. In Hovey, the Supreme Court specifically applied the Due Process Clause to fair trial guarantees, holding that due process "secures an 'inherent right of defense'". This doctrine eventually came to protect the defendant's ability to "present exculpatory evidence and testimony of witnesses". For example, the Court in Brady v. Maryland used the Due Process Clause to require the prosecution in criminal proceedings to disclose evidence that is favorable to the defendant prior to a trial. The Court's due process jurisprudence was expanded with the 1948 decision in In re Oliver which revised the breadth of the fundamental fairness doctrine. The Court wrote: In Washington v. Texas, the Supreme Court held that the Clause barred a state law that made persons charged or convicted as co-participants in a common crime incompetent to testify on behalf of one another. This was a holding based on the Due Process Clause, a departure from the Oliver cases. Chief Justice Earl Warren, who wrote the majority opinion, stated that compulsory process was critical to the very ability to "present a defense... defendant's version of the facts". This broad right was necessary to note as its absence would make the right to compel witnesses futile. However, in Taylor v. Illinois, the Court rejected a challenge to witness preclusion rules, holding that the Clause did not provide for an "absolute" right for defendants. The Court held that "The Compulsory Process Clause provides with an effective weapon, but it is a weapon that cannot be used irresponsibly". There are "countervailing public interests" which weigh against an absolute position of applying the Clause; this signaled a major turn since Washington two decades earlier.
Remedies
In modern practice, a violation of the Compulsory Process Clause leads to the reversal of a conviction unless the original error is "harmless". This occurs because the exclusion of defense evidence can "significantly undermine fundamental elements of the defense". The remedy is not automatic reversal only because not every Sixth Amendment error is automatically a Due Process error.