A lawyer for James B. Comey, the former F.B.I. director, said at his arraignment on Wednesday that the defense team intended to file two motions to dismiss the case against him before it goes to trial.

The lawyer, Patrick J. Fitzgerald — himself a former high-powered Justice Department prosecutor — indicated that the defense would accuse the Trump administration of abusing prosecutorial power and raise a technical challenge to the legitimacy of the prosector President Trump installed to bring the case, Lindsey Halligan.

Here is a closer look at those types of challenges.

What is the abuse of prosecutorial power claim?

One of the motions to dismiss the case that the Comey defense team intended to make, Mr. Fitzgerald said, would be based on a claim that the charges amounted to “vindictive prosecution” and “selective, retaliatory prosecution at the direction of President Trump to silence” Mr. Comey.

These are closely related concepts involving abuse of prosecutorial power in violation of the Constitution’s guarantee that everyone has a right to due process and equal protection under the law.

What is vindictive prosecution?

It is a type of prosecutorial misconduct that involves bringing charges for improper reasons, such as retaliation for an exercise of constitutional rights. The idea is that such a case would violate a defendant’s right to due process under the law.

It is not enough, legal specialists say, to show that prosecutors focused on a particular person, since there are many examples of special counsels being appointed to investigate and charge a particular matter. The defense would have to show that the reason prosecutors focused on Mr. Comey was for something like retaliation over his exercise of constitutional rights.

Mr. Trump has long assailed Mr. Comey, whom he fired as F.B.I. director in 2017 amid the Russia investigation, and has cast him as an adversary. Mr. Comey has frequently criticized Mr. Trump. Mr. Fitzgerald’s mention of Mr. Trump trying to “silence” Mr. Comey suggested he would argue that Mr. Comey was being retaliated against for exercising his First Amendment rights.

What is selective prosecution?

It is a type of prosecutorial misconduct that involves singling out one person for charges when other people who committed similar offenses are not charged. The idea is such a case would violate a defendant’s right to equal protection under the law.

A defendant would have to show that the same prosecutor’s office — here, the U.S. attorney in the Eastern District of Virginia — looked at other cases that were identical to Mr. Comey’s and decided not to bring charges, and that the reason for the difference was discrimination based on some constitutionally protected characteristic.

Specifically, the Supreme Court has said that selective prosecution violates the Equal Protection Clause, if the reason for treating one defendant differently from other people who might be charged is “deliberately based upon an unjustifiable standard such as race, religion or other arbitrary classification.”

“There is an interesting question of whether people who are opposed to Trump are a political class that is protected against selective prosecution,” said David A. Sklansky, a Stanford University criminal law professor. “I would think it would be.”

He pointed to a 1985 case in which a defendant claimed he was being charged for exercising his First Amendment right to protest against the military draft. In that matter, a federal district judge agreed and threw out the charge. But the Supreme Court later held that the case could go forward because the defendant had not proved he had been singled out “because of his protest activities.”

What are Comey’s chances of winning?

Criminal defendants in politically high-profile cases often raise such claims, but they rarely succeed. One reason is that in the American justice system, prosecutors have broad discretion to choose how to handle a criminal case, from selecting more or less harsh charges, striking a plea bargain or bringing no charges at all.

Samuel W. Buell, a Duke University criminal law professor, said that courts defer to the executive branch about charges, and cases of dismissing an indictment for wrongful charging decisions “are so rare that it is almost impossible to find one.”

But, he said, the situation with Mr. Comey’s indictment was so unusual that he might have a chance.

Mr. Trump pushed Attorney General Pam Bondi to charge Mr. Comey with lying under oath as the five-year statute of limitations was about to expire for bringing charges over his congressional testimony. When the previous interim U.S. attorney, Erik S. Siebert, refused to seek an indictment because he viewed the available evidence as too weak, Mr. Trump forced him out and had Ms. Halligan, a former personal lawyer who had never prosecuted a case, installed in his place. She asked a grand jury to indict.

“This kind of claim is exceedingly difficult to prevail on as a basis to dismiss an indictment pretrial, but the sequences of events here as to how this went down with the statute of limitations looming is so extraordinary that this might be the case where vindictive prosecution works,” Professor Buell said. “The record is very bad for the government.”

What is the unlawful appointment claim?

Mr. Fitzgerald also said that he intended to file a motion to dismiss the case on the grounds that Ms. Halligan’s appointment as U.S. attorney was unlawful.

This is a technical argument that goes not to the merits of the charges or the motivation behind them, but to whether she had legitimate authority to ask a grand jury to indict Mr. Comey. If she did not, then a judge could throw out the indictment.

What are the circumstances of Halligan’s appointment?

Normally, a U.S. attorney is a Senate-confirmed position. When there is a vacancy that needs to be temporarily filled, the default rule is that the No. 2 official in the office serves as the acting U.S. attorney until the Senate confirms a new appointee. But federal law also allows an administration to put someone else into that role, with certain limitations.

One mechanism, which is apparently how Ms. Halligan was installed, is a statute that allows the attorney general to appoint an “interim” U.S. attorney for up to 120 days. The statute says that when that term expires, a federal court decides whom to appoint as the next interim, until the Senate confirms someone for the role.

Using this mechanism allows a president to simultaneously nominate that official to hold the role permanently. Mr. Trump has nominated Ms. Halligan for the role.

But Ms. Bondi had earlier appointed Mr. Siebert as an interim U.S. attorney, and after he served that 120-day term, a federal court appointed him as the U.S. attorney.

The question is how to interpret Mr. Siebert’s departure — as creating a new vacancy, starting the cycle over so that Ms. Bondi could appoint a new interim U.S. attorney, or as part of the same sequence, so that she probably could not, said Anne Joseph O’Connell, a Stanford University law professor who has written extensively about acting officials.

She said there was no definitive judicial precedent about how to interpret the interim U.S. attorney statute.

In 1986, after the interim U.S. attorney law was enacted, Samuel A. Alito Jr. — then a Reagan administration lawyer in the Justice Department’s Office of Legal Counsel — wrote that Congress seemed to intend a system in which after the expiration of a 120-day interim appointment, any “further interim appointments are to be made by the court rather than by the attorney general.”

What happens if the indictment is thrown out?

It is probably dead. One reason Mr. Trump was apparently pushing so hard to get someone to ask a grand jury to indict Mr. Comey over his September 2020 testimony was that the five-year statute of limitations to charge him with lying to Congress was about to expire.

Because that deadline has now passed, it would be difficult to revive the case against him with a new indictment. Prosecutors would have to find a more recent action, then portray the sequence as some kind of ongoing conspiracy by Mr. Comey to lie to Congress.

Notably, even the charge brought against Mr. Comey was something of a bank shot to get around an expired statute of limitations. Mr. Comey is being charged for saying in 2020 that he stood by something he had said in 2017 testimony, for which the deadline to charge him had long passed.

Minho Kim contributed reporting from Alexandria, Va.