National security expert tells CNN: 'Russia has had leverage over Donald Trump' for years
Russia's President Vladimir Putin called his summit with US counterpart Donald Trump "very successful." (AFP / Yuri KADOBNOV)

As more evidence of collusion between Russia and President Donald Trump emerged Friday, pundits wondered just how compromised the Trump administration is by the 2016 campaign's links to Russia.

Security expert Garrett Graff, author of The Threat Matrix: Inside Robert Mueller's FBI and the War on Global Terror, noted on CNN Monday that even without seeing Mueller's full report, it's clear from what we do know that we're looking at "the worst case scenario."

He noted that it's clear the Trump administration was compromised by Kremlin agents in a way that suggests Vladimir Putin has leverage over the President.

"From a counterintelligence perspective, the worst case scenario is to have a foreign power have leverage over your head of state, for them to have some sort of intelligence operation or even blackmail that can convince a head of state to act against their country's best interests," Graff observed.

"And what we already know from the Trump investigation by Special Counsel Robert Mueller, especially after these last ten days of revelations from Michael Cohen, Michael Flynn, and Paul Manafort, is that Russia has had leverage over Donald Trump over the last two years."