WASHINGTON — The trial of Paul Manafort was not about election conspiracy or presidential obstruction of justice. Michael D. Cohen pleaded guilty to crimes that had nothing to do with Russia’s campaign to sabotage the 2016 presidential race.

Yet the deepening legal peril for both men could have significant implications for the current investigation by the special counsel, Robert S. Mueller III.

The cases of both men are, at the moment, tangential to the central questions of Mr. Mueller’s inquiry: whether President Trump and his associates conspired with Russia’s election interference, and whether the president tried to obstruct the Justice Department’s investigation into the matter. But neither Mr. Manafort nor Mr. Cohen is believed to be cooperating with the special counsel — situations that could change now that they face years in prison.

Whether either man has anything of value to offer Mr. Mueller’s investigators is another question, and experts pointed out that the legal proceedings have dealt significant damage to the credibility of both. The team for Mr. Cohen, the president’s former lawyer, at least, has signaled a willingness to provide information to the special counsel in exchange for some kind of leniency.