A war of words between House Judiciary Committee Chairman John Conyers (D-Mich.) and former White House political director Karl Rove escalated to live fire Thursday, when Conyers subpoenaed Rove to testify before Congress on the prosecution of former Alabama Gov. Don Siegelman (D).

For several weeks, Conyers and Robert Luskin, Rove’s attorney, have exchanged increasingly acerbic letters in the wake of a television news report quoting Luskin as saying Rove would be willing to testify about the Siegelman case.

Several news stories have featured allegations that Rove directed federal prosecutors to pursue a bribery case against Siegelman. Rove has flatly denied any involvement in the case.

Luskin has rebuffed several requests from Conyers for Rove to testify on the Siegelman case, as well as broader issues of political influence at the Justice Department.

Luskin argues that the White House has already asserted executive privilege over the testimony of top officials in a dispute currently being litigated by the courts.

In a May 21 letter, Luskin argued that “While the Committee has the authority to issue a subpoena, it is hard to see what this will accomplish, apart from a Groundhog Day replay of the same issues that are already the subject of litigation.” Luskin argues that Rove is not a “free agent” in these matters, and is bound by whatever privilege the White House chooses to assert.

But Conyers replied on Thursday that “Mr. Rove, as a private party not employed by the government, is himself responsible for the decision on how to respond to the enclosed subpoena, which is a legally binding directive that he appear before the Committee on July 10.”

Judiciary ranking member Lamar Smith (R-Texas) accused Conyers of playing “partisan games” because the committee has refused Rove’s offer to answer written questions about the case. Smith said that if Rove is forced to testify, he will demand testimony from Jill Simpson, who is a primary source of the allegations against Rove.

Separately, Conyers also released a letter from the Justice Department indicating that “the Office of Professional Responsibility currently has pending investigations involving, among others, allegations of selective prosecution relating to the prosecutions of Don Siegelman” and several other Democratic officials.