Sen. Lindsey Graham will testify Thursday at the trial of Sen. Robert Menendez, the senator’s office said.

“Graham is testifying as a character witness for the defense and traveled to the trial at his own personal expense,” the South Carolina Republican’s office said in a statement. “He will testify about his service with Senator Menendez in the Senate. Graham’s testimony is unrelated to the underlying charges.” 

Menendez, a New Jersey Democrat, faces public corruption charges for allegedly using his influence as a U.S. senator to help a South Florida eye doctor.

A report from CNN said Sen. Cory Booker, a fellow New Jersey Democrat, is also expected to testify. A Booker spokeswoman did not immediately respond to request for comment.