In the context of Congress, it’s a privilege that can be granted to compel the testimony of a witness whom lawmakers really want to hear from. It means that the witness’s testimony cannot be used in any criminal prosecution.
2. Does Flynn’s offer mean he broke a law?
Not necessarily. He could be seeking safe haven from what Trump, his former boss, called .. https://www.bloomberg.com/politics/articles/2017-03-30/flynn-said-to-seek-immunity-to-testify-in-russia-investigations .. "a witch hunt." On the other hand, some have suggested that Flynn violated the Logan Act -- an obscure 1799 law prohibiting regular people from dabbling in international diplomacy -- in his December 2016 phone call with the Russian ambassador, Sergey Kislyak. The two men discussed new sanctions imposed by Barack Obama, who was still president. The possibility that Flynn wasn’t entirely forthcoming .. https://www.nytimes.com/2017/02/14/us/politics/fbi-interviewed-mike-flynn.html .. to the FBI about the scope of that phone call raises another potential legal liability for him.
3. Would that make Flynn off-limits to prosecution?
Not entirely. The immunity Congress grants, often called "testimonial" or "use" immunity, only means that the witness’s testimony can’t be used in a criminal prosecution. If there’s other evidence of a crime, the person can still be charged. Only the Justice Department can give a broader "transactional" immunity from being prosecuted.
4. Does Flynn’s offer mean he has dirt on others?
Again, not necessarily. He might, for example, be looking to clear his name or tell his side of the story before others tell it for him. Congress does have a way to get a sneak peek at what Flynn might say by asking him for a proffer .. http://apps.americanbar.org/litigation/committees/criminal/email/winter2012/winter2012-0402-risks-benefits-proffer-agreements-parallel-proceedings.html .. -- preliminary information that could then be used to expand the investigation. While a proffer by Flynn couldn’t be used against him, he could still be held criminally liable on the basis of other evidence. Adam Schiff, the top Democrat on the House Intelligence Committee, said any request for immunity will require "a detailed proffer of any intended testimony."
5. Can Congress grant immunity on its own?
It usually coordinates with the Justice Department, though their competing objectives sometimes get in the way. Congress wants to get information out quickly to respond to voter and media pressure for answers; prosecutors want to keep secret the information they gather, for a possible criminal case. In the case of hearings before Senate or House committees, a grant of immunity requires a two-thirds vote of their members.
6. What happens if Congress and prosecutors disagree?
That’s what happened in the drawn-out investigation of the Iran-Contra affair .. http://www2.gwu.edu/~nsarchiv/NSAEBB/NSAEBB210/index.htm , the secret effort under President Ronald Reagan to aid right-wing guerrillas in Nicaragua with money raised from the sale of arms to Iran. Congress granted immunity to compel the testimony of Oliver North, who had played a central role as a staff member with the White House National Security Council. North later was convicted of criminal charges but successfully appealed by arguing that his criminal trial had been tainted, despite prosecution efforts to shield it from his immunized congressional testimony.
7. Do lawmakers care if they spoil a potential prosecution?
Some do. The House Democratic leader, Nancy Pelosi, said Flynn shouldn’t be allowed to take "an immunity bath," as North did. Schiff said that while Flynn’s testimony "is of great interest to our committee, we are also deeply mindful of the interests of the Department of Justice in the matter."