Trump ally and former legal adviser face grand jury in NY investigation.

Robert Costello, a lawyer allied with Donald Trump, is expected to testify before a New York grand jury on Monday regarding hush money paid during Trump's 2016 campaign. Costello was asked to appear by the Manhattan district attorney's office after he said he had information raising questions about the credibility of Michael Cohen, a key witness in the investigation. Trump has criticized the New York investigation and directed particularly hostile rhetoric toward Manhattan District Attorney Alvin Bragg. It is unclear whether Costello's testimony has any potential to change the course of the grand jury probe.