A row is developing over whether General Michael Flynn, Donald Trump's former national security adviser, should be given immunity in exchange for testifying at a congressional investigation into Russian interference in America's presidential election.
The development comes as Mr Flynn, who is being investigated for his connections to Moscow, faced questions over why he failed to disclose meetings with a Russian and British woman reported to have trusted contacts in Moscow spy agencies.
Mr Flynn has asked for protection from what his lawyers have called "unfair prosecution" if he testifies before the intelligence committees of the US Senate and the House of Representatives.
Robert Kellner, his lawyer has said Mr Flynn "has a story to tell" and is willing to be interviewed about the Trump campaign's possible ties to Russia.
This might have seemed an ominous development for the White House. But Donald Trump responded on Friday by actively encouraging the move, and calling the investigations into Mr Flynn and his presidential campaign a political "witch hunt" instigated by Democrats.
"Mike Flynn should ask for immunity in that this is a witch hunt (excuse for big election loss), by media & Dems, of historic proportion!" he tweeted.
Mr Flynn was forced to resign from his post after only 24 days, when it emerged he had lied to Mike Pence, the vice president, about conversations he held with Sergei Kislyak, the Russian ambassador to the United States.
Mr Flynn's connections to Russia have also been questioned following the revelation that he was paid $45,000 (£35,800) plus expenses to speak at the 10th anniversary gala of the Russia Today, the state television network in Moscow in December 2015, while he was already an adviser to Trump.
His testimony could reveal more about the nature of his conversations with Mr Kislyak, and give potentially valuable insights into activities by other members of Mr Trump's campaign staff, who are also under investigation.
But Adam Schiff, a ranking Democrat congressman on the House of Representatives intelligence committee, said it was too soon to consider immunity requests.
"As with any investigation - and particularly one that grows in severity and magnitude by the day - there is still much work and many more witnesses and documents to obtain before any immunity request from any witness can be considered," Mr Schiff said in a statement.
Mr Schiff said the panel would discuss any request with the Justice Department and the Senate Intelligence Committee, describing such a request "a grave and momentous step."
An unnamed congressional official reportedly told NBC news that the option of immunity was "not on the table" at the moment.
In September last year, when he was a Trump campaign adviser, Mr Flynn addressed the issue of immunity in relation to aides of Hillary Clinton seeking it in return for talking to the FBI about her email server. Mr Flynn said in a TV interview: "When you are given immunity that means you probably committed a crime."
At the time Mr Trump himself told a rally in Wisconsin: "The reason they get immunity is because they did something wrong. If they didn’t do anything wrong they don’t think in terms of immunity. If you are not guilty of a crime what do you need immunity for, right?"
Concerns were also raised on Friday about Mr Flynn's failure to disclose contacts with a Russian-British academic at an intelligence seminar in Cambridge in 2014.
Mr Flynn met Svetlana Lokhova at The Cambridge Intelligence Seminar, a forum for intelligence professionals attended by leading experts including Sir Richard Dearlove, the former head of MI6, and Prof Christopher Andrew, the official MI5 historian, the Wall Street Journal reported.
Ms Lokhova, who holds Russian and British citizenship, is a graduate student of Prof Andrew.
At the time, Mr Flynn was one of the top US spies and the director of the Defense Intelligence Agency. Mr Flynn would have been expected to “self report” any conversation with links to an “adversary” country, such as Russia.
Boris Volodarsky, a former GRU agent and a historian of the Soviet and Russian secret services who knows both Ms Lokhova and Mr Andrew, said to his knowledge she does not have an intelligence service background.
But he cautioned: "You can never know whether someone has been sent by the KGB."