The former CIA director, John Brennan, said there were enough contacts between members of the Trump campaign and Russian intelligence services by last summer to justify an investigation by the FBI. "But I know there was a basis to have individuals pull those threads".
Mr Brennan's testimony before the House Intelligence Committee gave a much clearer view of how seriously United States intelligence took the Russian threat, and why the Federal Bureau of Investigation began investigating it in July a year ago, well before the country was aware of the allegations.
Warner said one subpoena had been served and that he expected the second one to be served Tuesday evening.
The survey was conducted from May 17 to May 23, meaning that all interviews happened after the appointment of a special counsel to oversee the Justice Department's Russian Federation investigation.
USA media reports have alleged that Trump pressured his national security chief and his director of national intelligence to publicly deny the Russian Federation collusion allegations.More news: S. African labor federation bans Zuma from addressing its meetings
Efforts in both chambers of Congress to get information from ousted national security adviser Mike Flynn are escalating this week after Flynn refused requests from the House and Senate Intelligence Committees to testify and turn over documents on his contacts with Russian officials.
Coats and Rogers reportedly rejected the president's requests.
Kremlin insiders identified former Trump campaign manager Paul Manafort and former national security adviser Michael Flynn as targets during talks last summer that were intercepted by security agencies and passed to the Federal Bureau of Investigation, it is claimed.
Separately, Carter Page, a former foreign policy adviser to Trump's presidential campaign, told Reuters via text message that he would testify before the House Intelligence Committee but was "still working out details".
Warner and the panel's chairman, Republican Richard Burr, said the committee would take three actions in response to Flynn's refusal to respond to their subpoena, the two subpoenas to his businesses, and a letter to Flynn's attorney pushing back against his refusal to comply. Everything but immunity, he added.More news: Singapore conduct joint naval exercises, China voices concern
He spoke vaguely about contacts between Trump associates and Russian officials, without giving names, saying they "raised questions in my mind about whether Russia was able to gain the cooperation of those individuals". When he left office, "I had unresolved questions in my mind as to whether or not the Russians had been successful in getting US persons involved in the campaign or not to work on their behalf".
FILE - In this February 13, 2017 file photo, Mike Flynn arrives for a news conference in the East Room of the White House in Washington. He said the Russian official denied such interference but also said he would relay the concern to President Vladimir Putin.
Read the full New York Times report here.
And before such intelligence is shared, the country that provided it must be warned so as not to jeopardize sources or methods, Brennan said.
The Russian officials thought the pair could be used to influence Mr Trump's views on Russia.More news: Vermont governor vetoes marijuana bill, wants changes made