His comments came two days after he yanked the security clearance of former CIA Director John Brennan, saying he had to do "something" about the "rigged" federal probe of Russian election interference.
Hayden made his remarks in a Friday interview on CNN's "New Day."
The list of former senior intelligence officials who signed the letter includes James Clapper, a former Director of National Intelligence, and seven CIA Directors including Robert Gates, William Webster, George Tenet, Porter Goss, Michael Hayden, Leon Panetta and David Petraeus. At a summit in Finland last month, Trump drew criticism and outrage when he told reporters he accepted Putin's denial that Russian Federation had intervened in the 2016 presidential election - a stance in direct conflict with the USA intelligence community's position.
Trump said that in addition to Brennan, the security clearances of nine other former officials are under review.
Departing for NY on Friday, President Trump said he did not know McRaven, but added that he had received a "tremendous response from having done that because security clearances are very important to me". He said the only question now is whether the collusion that took place "constituted criminally liable conspiracy".
In August 2016, just two days after Brennan briefed Senator Harry Reid and other members on Russian interference in the election, the Nevada senator wrote a letter to then-FBI director James Comey, calling the FBI to investigate Trump's campaign. "Decisions on security clearances should be based on national security and not political views". "I've never respected him; I've never had a lot of respect", Trump said. "In some cases, they've lied before Congress".
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As Hill Reporter covered yesterday, legal analysts say that a president getting involved in the process of revoking security clearances, especially without going through the usual channels, is utterly unprecedented, and could result in legal battles to determine whether Trump actually has that power.
The White House announced Thursday that it was revoking the former Central Intelligence Agency director's clearance because of what press secretary Sarah Sanders called "unfounded and outrageous allegations".
Early this month, he admitted in a tweet that the Trump Tower meeting, which was arranged by his son, Donald Trump Jr., "was a meeting to get information on an opponent".