Retired Lt. Gen. Michael Flynn, fired as Trump’s national security adviser in February, announced Monday through his attorneys that he would not comply with a subpoena issued by the Senate Intelligence Committee for documents relating to the investigation into alleged Russian interference in the 2016 US presidential election.

In a letter to committee chairman Richard Burr and vice-chairman Mark Warner, Flynn’s lawyers said he would invoke his Fifth Amendment right against self-incrimination.

“The context in which the Committee has called for General Flynn’s testimonial production of documents makes it clear that he has more than a reasonable apprehension that any testimony he provides could be used against him,” Flynn’s attorneys wrote.

The subpoena called on Flynn to supply a list of all contacts he had with Russian officials between June 16, 2015 and January 20, 2017, when Trump took office as president, as well as any records of conversations that took place during these contacts.

The investigation of Flynn is part of the internecine conflict within the ruling class that has pitted the Trump administration against the Democratic Party, and sections of the military-intelligence apparatus and the media.

In citing the Fifth Amendment to avoid even producing documents about conversations, Flynn’s lawyers were in effect arguing that the conversations themselves could be construed as criminal acts. Flynn would not discuss them without receiving immunity for his testimony from the committee, they added.

They also cited the appointment of former FBI Director Robert Mueller as a special prosecutor investigating claims of collusion between the Trump campaign and the Russian government, claiming that this appointment gives rise “to a constitutional right not to testify.”

The letter also cited the unprecedented scale of the media campaign over the alleged Russian intervention, fueled by leaks from within the military-intelligence apparatus.

“Multiple Members of Congress have demanded that he be investigated and even prosecuted,” Flynn’s lawyers wrote. “He is the target on nearly a daily basis of outrageous allegations, often attributed to anonymous sources in Congress or elsewhere in the United States Government, which, however fanciful on their face and unsubstantiated by evidence, feed the escalating public frenzy against him.”

Burr and Warner issued a joint statement declaring that while they recognized Flynn’s constitutional right to invoke the Fifth Amendment, “We will vigorously pursue General Flynn’s testimony and his production of any and all pertinent materials pursuant to the committee’s authorities.”

Flynn was fired by Trump February 13, allegedly for lying to Vice President Mike Pence about the content of his telephone discussion with Russian Ambassador Sergey Kislyak in late December 2016. Based on Flynn’s assurances, Pence went on several Sunday television interview programs to declare that Flynn had not discussed with the Russian official the sanctions imposed on Russia by the Obama administration for its alleged interference in the US elections.

US intelligence intercepts of the Flynn-Kislyak telephone calls, apparently derived from routine monitoring of the Russian official, demonstrated that Flynn had lied about the content of the discussion, and the White House was notified by acting Attorney General Sally Yates, although Flynn was not fired for another 18 days.

Senate and House Democrats have been especially insistent about obtaining testimony from Flynn, formerly one of Trump’s closest aides, in the hopes that it would point more directly at Trump himself, and that Flynn would admit to being an intermediary between the candidate or president-elect and Russian officials.

The potential charges against Flynn do not, however, arise from the incident that led to his firing, since one White House official lying to another is not a crime. Flynn could face charges for failing to disclose his financial relationships with a Turkish businessman, who was acting on behalf of the Turkish government, as well as various payments made to him by Russian media and business interests before he became an adviser to the Trump campaign.

Also Monday, the top Democrat on the House Oversight and Government Reform Committee, Rep. Elijah Cummings of Maryland, claimed in a letter to committee chairman Rep. Jason Chaffetz that Flynn had lied to the Pentagon about who paid for his trip to Russia in December 2015 where he spoke at a gala hosted by the media company RT. Retired military officers must report income from any foreign country.

Cummings made the letter public almost immediately, as a way of further intensifying the political pressure on the Trump administration and the Republican leadership of the various congressional committees investigating the claims of Trump-Russia collusion.

Late on Monday, the Washington Post reported that President Trump had asked two top intelligence officials for help against the ongoing FBI investigation into charges that Trump campaign officials had coordinated actions with the Russian government.

Citing “two current and two former officials, who spoke on the condition of anonymity,” the Post said that Trump had separate discussion with Director of National Intelligence Daniel Coats and Admiral Michael S. Rogers, the director of the National Security Agency, asking them to publicly deny that there was any evidence of collusion during the 2016 election campaign.

The discussions took place shortly after Comey testified on March 20 before the House Intelligence Committee and publicly confirmed, for the first time, the existence of the FBI investigation. Both officials refused Trump’s request, and both considered the request improper, with Rogers documenting the request contemporaneously in an internal memo. The requests could well be considered additional acts of obstruction of justice by Trump in the investigation by special counsel Robert Mueller.

Coats and Rogers are both considered closer to Trump than other intelligence agency officials: Coats is a former Republican senator, appointed DNI by Trump, who had only been in office a few days. Rogers is a holdover, having first been appointed by Obama, but it was widely known that Obama did not intend to reappoint him, while Trump interviewed him for possible promotion to DNI before deciding instead to keep him at the NSA and appoint Coats instead.