WASHINGTON (AP) - A lawyer for former national security adviser Michael Flynn says he's in talks with congressional committees to testify before them in exchange for immunity from prosecution. Those committees are investigating Russian influence in the 2016 presidential election and potential ties between Russia and associates of President Donald Trump.

Trump's attorney, Robert Kelner, said Thursday night that "no reasonable person" would agree to be questioned "in such a highly politicized, witch hunt environment without assurances against unfair prosecution." Trump echoed that sentiment Friday on Twitter, encouraging Flynn to seek immunity from a "witch hunt."

Some questions and answers about the process:

Q: What does it mean to receive immunity, and who can give it?

A: An immunity grant generally shields a witness from prosecution for statements he or she makes to the government.

Congress is empowered to give immunity to witnesses who might otherwise be inclined to avoid a committee hearing, protecting them from having their statements later used against them in a criminal prosecution.

The Justice Department, too, can offer different forms of immunity. One type, for instance, protects a witness from prosecution for any offense related to the testimony, while another, more narrow form simply bars the government from using someone's testimony against them.

The process of seeking immunity generally involves a person describing to the government what information he or she would be able to provide, a conversation known as a proffer. Investigators may decide immunity is worth it if it's the only way to secure a witness's testimony against a higher-value target, or if the testimony is seen as indispensable in resolving unanswered questions.

Plenty of high-profile witnesses have requested immunity for congressional testimony, from high-ranking federal government officials to professional baseball stars, though not everyone has received it.

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Q: If a witness seeks immunity, doesn't that mean he or she is probably guilty of a crime?

A: Not at all.

Since witnesses are under no obligation to speak with the FBI, it's fairly standard for them - through their lawyers - to demand immunity as an unwavering condition for any kind of conversation they agree to have.

Seasoned lawyers often see no benefit to cooperating with the government without such an agreement, especially since it's impossible to predict with certainty how the interview will go, what sort of statements or activities investigators will home in on, or whether any vaguely worded questions will trip up their client or prompt an unexpected answer or one unfavorable to their own interests.

"The easiest way to not incriminate yourself is to keep your mouth shut," said Washington lawyer Stephen Ryan, a congressional investigations expert.

Sometimes immunity will be granted if investigators believe a deal is the only, or at least the fastest, way to get the information they need. It can be especially palatable to the Justice Department if the person seeking immunity was never really at risk of prosecution in the first place, or if it represents the best chance to secure the cooperation of an otherwise wary witness whose insight is seen as critical.

The IT expert who set up Hillary Clinton's email server received limited immunity from the Justice Department. Her chief of staff also received a limited form of immunity because FBI agents wanted to inspect her computer.

Still, in a nation's capital consumed by optics, there's no doubt that an immunity request can make someone appear like he or she has something to hide.

Flynn himself allowed as much last year about the immunity deals in the Clinton email investigation, saying in a television interview, "When you are given immunity, that means that you have probably committed a crime."

That wasn't necessarily true then, and it's not any more true now that Flynn himself is seeking congressional immunity.

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Q: Why might Flynn in particular seek immunity?

A: It's already known that he's attracted the attention of law enforcement authorities.

Flynn was interviewed by the FBI in the early days of the Trump administration about communications he had during the transition period with the Russian ambassador.

He and his firm also recently registered with the Justice Department as foreign agents for lobbying work conducted on behalf of a company owned by a Turkish businessman. That businessman, Ekim Alptekin, has told The Associated Press that the registration was made under pressure from the Justice Department.

The Foreign Agents Registration Act requires people acting as agents for a foreign principal to publicly disclose that relationship.

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Q: If Congress chooses to grant immunity, what impact might that have on any criminal investigation?

A: It's not clear, though there are long-established restrictions on the Justice Department's ability to use any statements given to Congress under immunity in any future criminal prosecution.

Rep. Adam Schiff, the top Democrat on the House intelligence Committee, said Friday his panel was "deeply mindful of the interests of the Department of Justice in the matter."

Though it's not an impossible burden to meet, Justice Department prosecutors would inevitably have to prove that any case they bring did not rely on statements made to Congress.

Ryan said there's no doubt that a grant of congressional immunity can negatively affect a simultaneous criminal investigation.

A congressional committee, he added, has to balance the need to not interfere with a criminal investigation with its own interest in getting information out to the American public.

That was a stumbling block in the 1980s-era prosecutions of Iran-Contra affair figures Oliver North and John Poindexter, whose convictions were set aside following concerns from judges that witnesses in their criminal cases had been unduly affected by their congressional testimony.