A former top aide to Donald Trump’s presidential campaign will plead guilty to fraud-related charges within days — and has made clear to prosecutors that he would testify against Paul Manafort, the lawyer-lobbyist who once managed the campaign.

The change of heart by Trump’s former deputy campaign manager Richard Gates, who had pleaded not guilty after being indicted in October on charges similar to Manafort’s, was described in interviews by people familiar with the case.