Bush has order his former counsel Harriet Miers to not respond to the Congressional subpoena.
You can’t do that.
You can show up in response to the subpoena and claim some sort of executive privilege (see Taylor, Sara), or you can show up and lie (see, Gonzales, Alberto). But you just can’t order someone to not show up, because that’s a felony:
18 U.S.C. Sec. 1505 : … Whoever corruptly … influences, obstructs, or impedes … the due and proper exercise of the power of inquiry under which any inquiry or investigation is being had by either House, or any committee of either House or any joint committee of the Congress … [s]hall be fined under this title, [or] imprisoned not more than 5 years … or both.
18 U.S.C. Sec. 1515(b): As used in section 1505, the term "corruptly" means acting with an improper purpose, personally or by influencing another, including … withholding, [or] concealing … information.