within the timeframe for response, the chair of the committee may issue a subpoena to the senior responsible official for any unproduced records or information as to which no objection was filed, and to any designated witness to which no objection was filed. (d) With respect to any portion of the written request for documents and witnesses to which timely objection was made, a subpoena to the senior responsible official and to designated witnesses, may be issued, following conclusion of the negotiations referred to in paragraph (b), by— (1) the chair, upon 48 hours notice to the ranking member, unless the ranking member objects during that period