ATLANTA -- Former US Senator Sam Nunn says president Trump should expect two years of investigation into his campaign’s ties with Russia – now that a special counsel is investigating. Nunn watched three major scandals in Washington first-hand – and says this may be the most dangerous of them all.

Sam Nunn became a US senator in 1972 as Watergate was starting to flower. But he also saw scandals embroil the Reagan and Clinton administrations. None of them involved a superpower until this one.

"Because of the Russia involvement, it’s much more complex and much more dangerous," Nunn said Friday.

Nunn says Russian involvement in the November election, and the investigation thereof, can’t obscure the fact that the US and Russia need to work together to avoid military conflicts and nuclear misfires.

"It's very important now with all the moving parts and dangers in the world, to make sure the State Department and the Department of Defense and their leaders don’t get bogged down in this investigation. Because it’s going to go on for two years," Nunn said. "We’ve got to work with the Russians on a lot of questions," including Syria, Ukraine and North Korea.

Nunn was in Washington for Watergate, Iran Contra, and Whitewater – and he has some friendly advice for President Trump.

"If I was giving any advice to the White House I would say, look at how the Reagan administration handled the Iran Contra. And learn some lessons there," Nunn said. Of those three scandals, it was the only one that didn't produce a presidential impeachment or resignation.

Nunn says Reagan hired his own lawyer to deal with committees investigating Iran Contra, separating the scandal from ongoing governance.

Nunn says Reagan also wasn’t afraid to say it when he was wrong.

"There was a touch of humility and contrition that came out of President Reagan. I think this White House needs to understand that," Nunn said.

"I don’t think people expect a president to be perfect. But they do expect him to acknowledge mistakes when they're made and to correct those mistakes. And they don’t expect a president to be in denial of everything even when the facts indicate otherwise," Nunn said.