Washington ? Lawmakers investigating last year’s firings of eight U.S. attorneys took aim at the White House on Wednesday, subpoenaing the Justice Department for all related e-mails of President Bush’s political adviser Karl Rove.

The development is one of several that could increase pressure on the Bush administration to explain how involved White House officials were in the unusual order to fire several of the president’s top prosecutors and why.

Democrats are investigating whether the firings were improperly motivated by Republicans’ concerns about corruption probes or Democratic voter turnout in battleground election states.

Meanwhile, former Deputy Attorney General James Comey, who resigned in August 2005, is scheduled to testify today before a House judiciary subcommittee. Congressional aides said he could challenge the Justice Department’s assertions about performance problems among some of the ousted U.S. attorneys.

The same House panel on Wednesday released damaging new written responses from six of the ousted U.S. attorneys who earlier had testified publicly.

In them, the former prosecutors elaborated on their assessments that the firings were politically motivated.

In one statement, Carol Lam, the former U.S. attorney in San Diego, wrote that Deputy Attorney General Paul McNulty declined to respond to her questions about her removal because he didn’t want to give her an “answer that ‘would lead’ me down the wrong route.”

McNulty’s chief of staff, Michael Elston, also told her that she might be replaced by a Justice Department official who wasn’t from her office, she wrote. The candidate, whose name Elston didn’t reveal, wasn’t expected to go through the regular selection process in California.

The decision by Senate Judiciary Committee Chairman Patrick Leahy, D-Vt., to subpoena the Rove e-mails suggests lawmakers are running out of patience with the White House and may be moving closer to subpoenaing Rove directly, which could trigger a court battle.

“We not only need his documents, we also need his testimony,” said Sen. Charles Schumer, D-N.Y., a member of the panel.

Leahy said he took the step only to secure the e-mails after Gonzales twice declined to turn them over voluntarily. The subpoena gives Gonzales a May 15 deadline. If he doesn’t comply, Leahy said, he’ll be asked to appear before the panel to answer questions.