Former Nixon counsel John Dean said Tuesday that growing concerns about former Donald Trump campaign adviser Paul Manafort and his possible ties to Russia have "an awful lot of the sound and look and feel of cover-up."

"People not disclosing," Dean, who was involved in the Watergate controversy of the 1970s, told Don Lemon on CNN. "Denying. Dissembling on many facts.

"Looks like cover-up going on."

Manafort — who has lobbied for companies the Philippines, the Democratic Republic of Congo and the Ukraine — denied Monday any connections between himself and the Russian hacking of the Democratic National Committee and other party operatives last year.

The statement came after FBI Director James Comey told Congress the agency was investigating possible coordination between the Trump campaign and Russia during the presidential election.

Virginia Sen. Mark Warner said Tuesday "we have to talk to Mr. Manafort" as part of the Senate Intelligence Committee's probe into Russian activities.

"We're going to need to bring him in," the panel's ranking Democrat told CNN's Erin Burnett.

Dean told Lemon he was surprised top Republican senators – such as John McCain of Arizona and Lindsey Graham of South Carolina – are raising concerns about Manafort's alleged ties.

"It is encouraging that somebody on The Hill is taking a little distance and not being simply a shield for the White House," he said. "By and large, the Republicans are giving the White House an awful lot of cover."

His advice to President Trump: "Lawyer up."

"He's got a rookie White House counsel, who I don't think has deep criminal law experience," Dean said. "That's how the mistakes were made in the Nixon White House."