At least two of the agents are expected to testify on Capitol Hill Thursday.The FBI has revoked the security clearances of three agents for issues related to the Jan. 6 attack on the U.S. Capitol, according to a letter from the bureau to congressional investigators obtained by ABC News. One of the agents was among the pro-Trump mob at the U.S. Capitol, according to the FBI, and the two others are alleged to have hindered investigative efforts. At least two of the agents -- Steve Friend and Marcus Allen -- are expected to testify Thursday before the Republican-led House select...