WASHINGTON — Former President Donald J. Trump responded on Friday to a promised subpoena from the House committee investigating the Jan. 6 assault with a lengthy, rambling letter that attacked the panel’s work, reiterated false claims of widespread voting fraud and presaged a potentially bruising battle over whether he would be compelled to testify about his role in the riot and his efforts to subvert the 2020 election. In a 14-page missive that did not address whether he would comply with the subpoena, Mr. Trump perpetuated the same lies that had fueled the attack and boasted about the size of...
