She added that Trump had hired Manafort in 2016, "to handle the delegate process" during the Republican National Convention, "and he was dismissed not too long after that."
The White House also addressed the guilty plea of George Papadopoulos, a former foreign policy advisor on Trump's presidential campaign. Sanders emphasized that Papadopoulos was an unpaid advisor who, she said, only attended one meeting with Trump during the campaign. "Any actions he took would have been on his own," Sanders said.
Sanders also said that Trump is not currently planning to dismiss special counsel Robert Mueller, despite calls from some Republicans that Mueller be fired. "There is no intention or plan to make any changes in regards to the special counsel," she said.
Manafort's former longtime business partner, Rick Gates, also was charged in the 31-page indictment, made public on Monday. Gates and Manafort both surrendered to authorities on Monday morning.
A spokesman for Manafort did not immediately respond Monday to a request for comment from CNBC.
The indictments mark a new phase in Mueller's investigation into Russian attempts to interfere in the 2016 presidential election. They also cap off a year of escalating legal problems for Manafort and Gates, who worked with Manafort for years on many of his foreign lobbying contracts.