WASHINGTON — President Donald Trump’s nominee for attorney general will tell senators “it is vitally important” that special counsel Robert Mueller be allowed to complete his Russia investigation, and said he believes Congress and the public should learn the results, according to remarks prepared for his confirmation hearing. William Barr also insisted in testimony he’ll deliver Tuesday to the Senate Judiciary Committee that Trump never sought any promises, assurances or commitments before selecting him to be the country’s chief law enforcement officer. In releasing written testimony ahead of his hearing, the Justice Department moved to pre-empt the most significant questions Barr is likely to face from Democrats on the panel — including whether he can oversee without bias or interference the final stages of Mueller’s probe into potential ties between Russia and the 2016 Trump campaign, and whether he will permit the findings to be made public. “I believe it is in the best interest of everyone — the President, Congress, and, most importantly, the American people — that this matter be resolved by allowing the Special Counsel to complete his work,” Barr said. He described Mueller, a former Justice Department colleague, as a friend he has known personally and professionally for 30 years.