Preet Bharara: Former Trump campaign adviser Papadopoulos 'almost certainly' has 'flipped'

Former Trump adviser is likely cooperating with investigators, Bharara said.

The charges against him send a message that “the Mueller team takes very seriously being lied to ... Lying to the FBI is a form of obstruction" of justice, said Bharara, who was part of a panel discussion on "This Week" about the Russia probe.

The special counsel's team "clearly feel very seriously about [obstruction], and some people should be worried,” said the former U.S. attorney for the Southern District of New York.

Starr agreed with Bharara that Mueller sent a message: “'Don’t lie to the FBI.'"

But Starr and Bharara disagreed on whether President Trump has “crossed the line" against interfering with an investigation.

In contrast, Starr said, Trump is "just spouting off" in his comments about the Justice Department and the Russia probe.

"He's expressing this frustration, but it's not crossing the line into criminality," Starr said.