Dan Rather arrives on the red carpet for the film "Truth" during the 40th Toronto International Film Festival in Toronto, Canada, 12 September 2015 Reuters/Mark Blinch

Former CBS Evening News anchor Dan Rather has said that the scandal unravelling around Russia's connection to US President Donald Trump may surpass Watergate.

"Watergate is the biggest political scandal of my lifetime, until maybe now," Rather wrote on Tuesday in a post on his Facebook page. "On a 10 scale of armageaddon for our form of government, I would put Watergate at a 9. This Russia scandal is currently somewhere around a 5 or 6, in my opinion, but it is cascading in intensity seemingly by the hour."

Rather said that what he sees unravelling in the Trump administration "may become the measure by which all future scandals are judged."

He called what had been revealed so far "chilling," and added that "if a scriptwriter had approached Hollywood with what we are witnessing, he or she would probably have been told it was way too far-fetched for even a summer blockbuster."

The assessment follows a series of leaks to the Washington Post and New York Times from intelligence, law enforcement, and other government officials revealed that Trump's senior national security adviser, Michael Flynn misled the vice president over contact with Russia.

The fallout saw Flynn dramatically resign on Tuesday (14 February) as turmoil within the Trump administration threatens to spin out of control.

"We got to a point ... where a level of trust between the President and General Flynn had eroded to the point where he felt he had to make a change," White House Press Secretary Sean Spicer said in a statement.

Anonymous officials also revealed to the New York Times on Tuesday that Trump's campaign team had repeated contacts with senior Russian intelligence officials during the 2016 US election campaign. In January President Trump said no one from his campaign had ever been in touch with Russia.

Watergate is the biggest political scandal of my lifetime, until maybe now. It was the closest we came to a debilitating...

Posted by Dan Rather on Tuesday, February 14, 2017

The revelations were borne out of ongoing investigations from the FBI and Senate Intelligence Committee into the issues.

"The White House has no credibility on this issue," said Rather, adding that America needs an independent investigation into the issues. "We deserve answers," he said, "and those who are complicit in this scandal need to feel the full force of justice."