Democrats in the U.S. Congress are using subpoenas and other investigatory powers to expose missteps by the administration of President Bush and push for policy changes even as they struggle at times to enact legislation.

Backed by hundreds of hearings that compel the administration's attention but often draw scant publicity, House and Senate Democrats are leaving their stamp on a range of governmental matters, without passing a bill.

Congressional inquiries have prompted the Federal Emergency Management Agency to test trailers used by displaced hurricane victims for toxic contamination. They triggered a Justice Department investigation into Attorney General Alberto Gonzales' role in firing federal prosecutors.

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Other probes spurred the Army to recover millions of dollars in overpayments to private security contractors in Iraq. And the mere threat of Democratic-run hearings prompted President George W. Bush, after months of resisting, to submit a controversial warrantless wiretap program to a special court's review.

Congress' oversight and investigative powers are especially vital to Democrats because a potent Republican minority in the Senate has kept them from passing legislation on issues such as immigration and an Iraq withdrawal plan.

"Maybe it's even more important than legislation," said Democratic Congressman Henry Waxman, a key player who chairs the House of Representatives' Oversight and Government Reform Committee.

Democrats' ability to conduct such hearings "has been the most important change since the 2006 election in terms of relations between the Congress and the administration," said Thomas E. Mann, a Brookings Institution scholar.

"I have no doubt the hearings have altered the course the administration has taken on a range of areas, including Iraq," Mann said.

The White House has complained bitterly about the sharp increase in congressional inquiries since Democrats took over the House and Senate in January.

"I would hope Congress would become more prone to deliver pieces of legislation that matter as opposed to being the investigative body," Bush said at an Aug. 9 news conference. "I mean, there have been over 600 different hearings, and yet they're struggling with getting appropriations bills to my desk."

Democrats call the inquiries long overdue after years of GOP-controlled congresses treating the administration with a light touch. "I don't think Congress is overdoing the oversight," Waxman said in an interview.

New or expanded congressional inquiries seem to pop up almost daily. On July 17, Waxman called on a former White House political aide to testify about trips made by top federal drug policy officials to help Republican congressional candidates in the 2006 campaign's closing weeks.

The aide, Sara Taylor, had appeared only a week earlier before a Senate panel that subpoenaed her testimony about the prosecutor firings.

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