Mr. Johnson has also become the leading Republican proponent of a revisionist effort to deny the motives and violence of the mob that breached the Capitol. At a Senate hearing to examine the events of that day, Mr. Johnson read into the record an account from a far-right website attributing the violence to “agents-provocateurs” and “fake Trump protesters.” On Saturday, he told a conference of conservative political organizers in Wisconsin that “there was no violence on the Senate side, in terms of the chamber.” In fact, Trump supporters stormed the chamber shortly after senators were evacuated.