A House Judiciary subcommittee today authorised subpoenas for Karl Rove, President Bush’s political adviser, and other senior White House officials in the investigation into the firing of eight United States attorneys. Democrats said the subpoenas, approved on a voice vote of the panel, would not be issued immediately but could provide leverage for Congress in trying to win the testimony of the aides being sought.Republicans on the subcommittee said they did not dispute the power of Congress to call the officials, but said the action was premature and smacked of politics. “The only purpose of the subpoenas is to the fan the flames and photo ops of partisan controversy,” said Representative Chris Cannon of Utah, the senior Republican on the subcommittee.President Bush and Congress appear to be headed toward a constitutional showdown over the demands for testimony and for internal White House documents. Under growing political pressure, the White House had offered to allow private interviews with Rove, Harriet E Miers, the former White House counsel; and two other officials. It also offered to provide access to e-mail messages and other communications about the dismissals, but not those between White House officials.Democrats promptly rejected the offer, which specified that the officials would not testify under oath, that there would be no transcript and that Congress would not subsequently subpoena them.Responding defiantly on Tuesday, Bush said he would resist any effort to put his top aides under “the klieg lights” in “show trials” on Capitol Hill, and he reiterated his support for Attorney General Alberto R Gonzales, whose backing among Republicans on Capitol Hill ebbed further. “We will not go along with a partisan fishing expedition aimed at honourable public servants,” the president told reporters in a brief and hastily convened appearance in the Diplomatic Reception Room of the White House.The pointed exchange was set off by a Democratic inquiry into whether the White House let politics interfere with law enforcement by dismissing eight of the nation’s 93 United States attorneys. The dismissals have created an uproar in both parties.