His statement on the issue was made in 2016.
The witnesses may be asked to testify in Paul Manafort's upcoming trial.
The indictment alleges the Russians aimed to influence the 2016 presidential election.
The Department of Justice announced a new indictment from Robert Mueller's team Friday, naming 12 Russian defendants.
According to Bloomberg, Robert Mueller is "making more use" of career prosecutors from U.S. attorneys' offices and the Department of Justice.
An article said Twitter was leaking the president's private messages to the Department of Justice and was caught in an "undercover sting." Nope.
A federal judge revoked Manafort's bail and ordered him to await trial in jail after special counsel Robert Mueller accused him of witness tampering.
A judge ordered the special counsel to identify unnamed individuals in the lobbying case against Donald Trump's former campaign chairman.
On Monday, the government filed a motion accusing former Trump campaign chairman Paul Manafort of witness tampering.
Robert Mueller's office says former Trump campaign chairman Paul Manafort tried to get potential witnesses to give false testimony.