President Donald Trump's former national security adviser, Michael Flynn, invoked his Fifth Amendment right against self-incrimination in rebuffing a subpoena Monday in the investigation into Russia's election meddling. Then a top House Democrat cited new evidence he said appeared to show Flynn lied on a security clearance background check.

With Trump himself in the Mideast on his first foreign trip as president, investigations into Russian interference in the 2016 campaign — and allegations of Trump campaign collaboration — showed no sign of slackening in Washington. Flynn's lawyers claimed an "escalating public frenzy" against the former aide justified declining the subpoena for his records.

The attorneys told the Senate intelligence committee Flynn will not turn over personal documents sought under the congressional subpoena nor otherwise comply as part of its investigation. Hours later, Rep. Elijah Cummings, senior Democrat on the House oversight committee, cited what he said were inconsistencies in Flynn's disclosures to U.S. investigators in early 2016 during his security clearance review.

Cummings said Flynn appeared to have lied about the source of a $33,000 payment from Russia's state-sponsored television network, failed to identify foreign officials with whom he met — including Russia's President Vladimir Putin — and glossed over his firing as chief of the Defense Intelligence Agency during the Obama administration. Cummings made his points in a letter asking the committee's chairman, Jason Chaffetz of Utah, to subpoena the White House for documents related to Flynn.

Flynn's own defensive crouch revealed the high legal stakes he faces as investigations intensify: a U.S. counterintelligence probe of Russia, a criminal investigation involving him and multiple congressional probes.

His attorney, Robert Kelner, declined to comment on the new assertions by Cummings.

Besides the "public frenzy," Flynn lawyers also said earlier in the day the Justice Department's appointment of a special counsel has created a legally dangerous environment for him to cooperate with the Senate panel's investigation.

Trump appointed Flynn, a retired U.S. Army lieutenant general and top military intelligence chief, as his top national security aide in January, only to fire him less than a month later. The White House said that Flynn had misled top U.S. officials, including Vice President Mike Pence, about his contacts with Russian officials, including Russia's ambassador to the U.S.

Democratic Rep. Cummings said Monday that Flynn repeatedly provided inconsistent or untruthful statements to U.S. security clearance investigators in January 2016 before the renewal of his credentials. The Trump administration has criticized the Obama administration for failing to properly vet Flynn during that period, but Cummings and other Democrats have blasted Trump and his team for failing to more carefully check Flynn's background before they brought him to the White House.

Cummings cited a report in March 2016 that he said showed the retired Army general telling authorities that payments he received for his 2015 trip to Moscow were paid by "U.S. companies." In fact, the oversight committee released detailed email and payment records months ago showing that the source of Flynn's payment of more than $33,000 was RT, the Russian state-sponsored television network that has been labeled a propaganda network by U.S. intelligence.

Flynn went to Moscow to appear at an RT gala, sitting at the head table with Putin. Flynn was paid $45,000 by RT for the appearance through his speaker's group, Leading Authorities Inc. After the firm's deduction, Flynn received the $33,000, according to records obtained by the committee.

Meanwhile, the Senate committee's subpoena to Flynn focused on his interactions with Russian officials. It sought a wide range of information and documents about his and the Trump campaign's contacts with Russians dating back to June 2015.

Flynn's response stressed that his decision to invoke his constitutional protection was not an admission of wrongdoing but rather a response to the current political climate in which Democratic members of Congress are calling for his prosecution. Even "truthful responses of an innocent witness" can give the government ammunition that could be used against him, the attorneys noted, quoting a 2001 Supreme Court ruling.

The attorneys noted that if Flynn complied with the committee's request, he could be confirming the existence of documents, an act that itself could be used against him.

Trump himself walked back into the Russia controversy during his visit to Israel after Prime Minister Benjamin Netanyahu, standing beside him, was asked Monday if he had any concerns about intelligence sharing with the U.S.

After Netanyahu responded — he said the cooperation was terrific — Trump volunteered that he "never mentioned the word or the name Israel" during his recent Oval Office conversation with top Russian diplomats.

That comment referred to revelations that he divulged classified information about an Islamic State threat in his May 10 meeting in the Oval Office with Russia's foreign minister and ambassador. U.S. officials have said the information originated with Israel. However, it has not been alleged that Trump told the Russians that Israel was the source.

Trump has defended Flynn since his ouster and called on him to strike an immunity deal because Flynn was facing a "witch hunt." The president's comments were in stark contrast to his harsh words during the 2016 campaign for people who received immunity or invoked the Fifth Amendment in the probe of former Secretary of State Hillary Clinton's use of a private email server.

"You see, the mob takes the Fifth. If you're innocent, why are you taking the Fifth Amendment?" Trump said during a September campaign rally in Iowa.

On Monday, one of Trump's top GOP supporters, New Jersey Gov. Chris Christie, told reporters during a news conference in Trenton that he had expressed concerns about Flynn during the presidential transition.

"If I were president-elect of the United States, I wouldn't let General Flynn in the White House," Christie said.

Flynn's decision does not fully close the door on future cooperation with the committee. Attorney Kelner said in March that Flynn wants to tell his story "should the circumstances permit," and he said it would be unreasonable for him to agree to be questioned "without assurances against unfair prosecution."

Flynn's letter comes less than two weeks after the committee issued a subpoena for his documents as part of its ongoing investigation into possible collusion between Russia and Trump's campaign. In addition to the Senate investigation, Flynn is also being investigated by other congressional committees, as well as an FBI counterintelligence probe and a separate federal criminal investigation in northern Virginia.

An additional complication for the congressional committees: If they move to grant Flynn immunity, they will likely have to enter into discussions with Mueller to determine whether that could impede the FBI's case.

Former CIA Director John Brennan is to testify in open and closed hearings Tuesday before the House intelligence committee, which is conducting its own investigation.

Associated Press writers Eileen Sullivan, Vivian Salama and Darlene Superville and Michael Catalini in Trenton, New Jersey, contributed to this report.

Read the letter here.

Associated Press writers Eileen Sullivan, Vivian Salama and Darlene Superville contributed to this report.