(Adds attribution, paragraph 8) By Patricia Zengerle and Richard Cowan WASHINGTON(Reuters) -Top advisers to then-President Donald Trump told him that his claims of widespread election fraud were unfounded and would not reverse his 2020 election loss, but he refused to listen, according to testimony on Monday at a hearing of the committee investigating the Jan. 6, 2021, riot at the U.S. Capitol. Close aides and family members said they told Trump that they found no merit in a wide range of often outlandish allegations that surfaced after his election defeat, including reports of a “suspicious s…