WASHINGTON — Special counsel Robert Mueller has brought additional charges against President Donald Trump’s campaign chairman and a longtime associate, accusing them of obstructing justice. The new charges were unsealed Friday against Paul Manafort and Konstantin Kilimnik just days after prosecutors accused the two men of attempting to tamper with witnesses as Manafort awaits trial of felony charges related to his work on behalf of Ukrainian interests. The indictment charges both men with obstruction of justice and conspiracy to obstruct justice related to contacts they had with two witnesses earlier this year. The witnesses, who had worked with Manafort as he represented a pro-Russian political party in Ukraine, have told the FBI that they believed Manafort and Kilimnik were trying to get them to lie about the nature of their work. Through a spokesman, Manafort has maintained his innocence. The spokesman, Jason Maloni, said Friday that Manafort and his attorneys were reviewing the new charges.