Paul Manafort’s long-time deputy has been called to the witness stand to testify against the former Trump campaign chairman.
Rick Gates has been regarded as a crucial government witness ever since he pleaded guilty last year and agreed to co-operate in special counsel Robert Mueller’s investigation.
Prosecutors will turn to Mr Gates for first-hand support of their accusations that Mr Manafort concealed millions of dollars in foreign income and later lied when he applied for bank loans.
Mr Manafort’s defence has sought to blame Mr Gates for any illegal conduct and accused him of embezzling millions of dollars.
Mr Gates and Mr Manafort worked closely together for years.
They were the first two people indicted by Mr Mueller’s grand jury.