Democrats on the House and Senate Judiciary committees have adopted a highly cooperative approach to their investigations into the Justice Department firing of U.S. attorneys, which could increase the lawmakers’ political leverage as they issue subpoenas for key witnesses and documents from the White House.

In a joint release on Wednesday, House Judiciary Chairman John Conyers (D-Mich.) summoned former White House legal counsel Harriet Miers to testify before his committee on July 12. Senate Judiciary Chairman Patrick Leahy (D-Vt.) ordered ex-White House political director Sara Taylor to talk to Senators on July 11.

Both chairmen also issued nearly identical subpoenas on Wednesday for White House documents related to the firing of nine federal prosecutors in 2006.

Both committees pointedly avoided issuing a subpoena to presidential adviser Karl Rove, who also has been implicated in the scandal. One senior Democratic aide noted that the timing was not yet right for such a move, explaining that Democrats were “building an investigation.”

The unified front has included coordinating witness interviews, subpoenas and even media relations — but it also is likely to result in a fierce legal battle over claims of executive privilege.

“We have two immovable objects moving towards each other and it does look like it will go to court,” said Abbe Lowell, the House Democrats’ counsel during the Clinton impeachment trial and an ex-Justice Department official.

“Both sides risk a ton when they go to court. The risk is that the White House gets told that a privilege it thought existed doesn’t,” Lowell added, which would “chip away” at a key presidential prerogative. “Congress gets the lesson that it’s not as powerful as it thinks it is.”

So far, Leahy and Conyers have coordinated the scheduling of key witnesses for public hearings, alternated their demands for documents and shared information from private interviews of key Justice Department officials. Majority and minority counsels for both chambers are present at such meetings.

Democrats in both chambers have accused the Justice Department and White House of ousting nine federal prosecutors in 2006 for improper political reasons. The furor over the scandal has increased with time, and some in Congress have called on Attorney General Alberto Gonzales to resign.

One House Judiciary Committee aide said the Justice Department may have unwittingly prompted the high level of House-Senate cooperation by insisting private interviews with department officials be held jointly.

There’s been a “huge amount of House-Senate cooperation, starting almost from the beginning,” the aide said.

“One reason ironically is the Justice Department has almost forced it in a way,” the aide added. “It became almost a necessity, even if we didn’t like each other, which we do.”

The House aide said that while there is no regular coordination, such as weekly meetings or phone calls between the two committees, there is consultation about important moves each chamber plans to take.

The aide added that while relations between the two committees and their staffs have always been cordial, the need to cooperate was intensified after the ousted U.S. attorneys actually testified before Congress and it became clear the probe would be a “major issue.”

There has not been significant overlap either with star witnesses such as Monica Goodling, the former counsel to Gonzales and White House liaison who resigned over her involvement in the scandal. Conyers’ committee granted Goodling, who had invoked the Fifth Amendment against self-incrimination, immunity for her testimony before the House committee (the only forum in which she testified).

And though both committees held public hearings featuring former Deputy Attorney General James Comey, his dramatic account of a hospital bedside showdown over the National Security Agency’s warrantless wiretapping program was only given before the Senate.

It was unclear Wednesday whether Taylor or Miers would comply with the subpoenas and appear before Congress. Neither they nor their representatives returned calls for comment on Wednesday.

Some Democrats speculated that their status as former White House aides made their claims to executive privilege weaker. But Lowell argued the privilege would still be intact for their communications while in the White House. And as former White House counsel, Lowell said, Miers could further claim attorney-client privilege with those she consulted on the matter.

As for the request for White House documents, spokesman Tony Fratto said the administration would would “review the subpoenas and respond appropriately.”

“The committees can easily obtain the facts they want without this confrontational approach by simply accepting our offer for documents and interviews,” Fratto said. “But it’s clear that Sen. Leahy and Rep. Conyers are more interested in creating media drama than getting the facts.”

Both Senate and House aides said the timing of Wednesday’s subpoenas was not specifically related to a new dump of documents by the Justice Department.

Those documents, released Wednesday night by the two chambers, gave further detail about the roles of Miers and Taylor in the prosecutor purge.

E-mails between former Gonzales Chief of Staff Kyle Sampson, who was in charge of compiling the prosecutor hit list, show Miers consulting Sampson about the confirmation process for interim U.S. attorneys.

They also portray Taylor as angry that Justice Department officials — specifically outgoing Deputy Attorney General Paul McNulty — involved the White House in the fight. Taylor criticizes former Eastern Arkansas U.S. Attorney Bud Cummins III as “lazy — which is why we got rid of him in the first place.”