By Richard Cowan and Patricia Zengerle 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 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. The committee is showcasing this testimony as part of a broader picture it aims to paint of a president trying to illegally hold onto power after losing the Nov. 3, 2020 election to Democratic President Joe Biden. Here are some key takea…