Henry Waxman, the most dogged of congressional committee chairmen, has been described by Republicans as 'the scariest man in Washington'.

Since the Democrats took control of the House and Senate in January, he has been in overdrive, launching inquiries into issues ranging from global warming to White House emails, and the one that concerns the congressman most - Iraq.

Nancy Pelosi, the House speaker, is the public face of the new Democrat-led Congress, but Mr Waxman is the embodiment of the pent-up release of Democratic energy, determined to harry George Bush in his last two years in office.

The Bush administration is feeling the squeeze, from the White House to the Pentagon, state department and various federal organisations. Mr Waxman is currently waiting for the response from the secretary of state, Condoleezza Rice, on whether she will give evidence about the run-up to the war in Iraq. He issued a subpoena last month demanding her presence before his committee and, though she has hinted she will not attend, he seems confident that she will.

In an interview in his office overlooking Congress, he said his main concern is to discover why Mr Bush took the country to war. The issue has been churned over by journalists, by books from insiders and in reports but Mr Waxman does not feel anyone has yet got to the heart of the matter.

"We have gone to war, lost thousands of people - Americans, British, many more Iraqis - and spent billions of dollars. The whole of the Middle East is in turmoil ... it is hard to know where you are going if you do not know how you got there."

He is aware of the label "the scariest man in Washington" and says he is amused rather than proud of it. "I do not think of myself as scary. I think people who are frightened are not frightened of me but of things they have done, the questions they do not want answered."

Mr Waxman is investigating why Mr Bush, in his state of the union address in 2003, only months before the invasion, cited British intelligence saying that Iraq had tried to secure uranium from Niger for use in a nuclear weapons programme.

"This issue is important to me. I voted for authorisation to go to war in Iraq on the claim that Saddam Hussein was developing nuclear weapons. I found out that before the war began, the CIA knew that claim was based on forgeries. We wrote to Bush and said 'Did [the CIA] ever tell the administration? If they did not, that would be maladministration."

He is not planning to call any British government officials to give evidence. The UK has never formally admitted that MI6 was wrong but privately acknowledges the information was untrue while insisting it was put together in good faith.

What matters to Mr Waxman is not that the intelligence was wrong and that the CIA had concluded it was wrong, but why Mr Bush chose to cite British intelligence in his speech. "To say British intelligence provided information was almost a way of being technically accurate but attempting to deceive," he said.

That is why he wants Ms Rice, who was national security adviser at the time, to give evidence. The CIA said that it told the White House that the British information was wrong, but she says she either did not see that or cannot remember seeing it.

He is investigating other aspects of the war too, from postwar reconstruction, and in particular the role of the US conglomerate Halliburton, to battlefield misinformation. As part of the latter, Private Jessica Lynch gave evidence to his committee last month that the Pentagon had misrepresented her as a heroine.

The committee inquiry is also looking into the death of Pat Tillman, an American football player who turned down a lucrative contract to go to war in Afghanistan. The Pentagon initially said he had died in heroic action against the Taliban, but it turned out he was killed by friendly fire. "The administration made up a wholly fictious story," Mr Waxman said.

Asked about the Bush administration's reputation as one of the most secretive - or dishonest - in US history, he said they had "at certain times come up with statements that turned out to be untrue and they must have known to be untrue, but I do not want to brand them as dishonest per se. I feel confident they have been the most secretive, even more than Richard Nixon."

Mr Waxman feels that the Republicans, who had control of both the House and the Senate during the first six years of the Bush administration, failed in their constitutional duty to hold the administration to account and contrasted the way in which they pursued Bill Clinton when he was in power.

He said that when he issued his subpoena for Ms Rice and two others, a Republican complained it was like living in a Stalinist country. Mr Waxman said that the Republicans had issued 1,000 subpoenas when Mr Clinton was in power.

He denied he was being similarly partisan, saying that such scrutiny was a necessary part of the checks and balances of the US system and that he wants to get more information on the record. "People want the truth," he said.