Dick Cheney used to be portrayed in cartoons as the ventriloquist of the administration, his hand inserted into a George W. Bush puppet. Now the cartoons of the vice-president have a darker tone, with his hands controlling various instruments of torture.

Mr Cheney's advocacy, however, is best understood not as a defence of torture but as a key battle in the war over presidential power. His views of executive power were forged during the US retreat from Vietnam at a time of congressional assertiveness on foreign policy. After September 11 2001 he saw a chance to implement ideas about expansive executive power that he had long embraced and swing the pendulum back towards the president.

In an ABC interview in January 2002, Mr Cheney set out his philosophy: "In 34 years, I have repeatedly seen an erosion of the powers and the ability of the president of the United States to do his job. One of the things that I feel an obligation on - and I know the president does too - is to pass on our offices in better shape than we found them."

His interest in the issue can be traced to his formative political years as chief of staff to President Gerald Ford from 1975. His promotion came amid growing public unease over Vietnam. In 1973, Congress passed the War Powers Act, forcing the president explicitly to consult and report back to them when committing troops overseas. In 1974 the Church committee flexed its authority over intelligence activities, sparked by revulsion against CIA dirty tricks in the 1960s and 1970s.

"He saw the power of the presidency emasculated under his watch, particularly with the inability to stay the course in Vietnam," says Vin Weber, a Republican strategist who has known him for 25 years. "He's been determined to reverse this ever since from the energy taskforce to national security. I believe the current issue is less about the value of torture than about an imperative to preserve and strengthen the presidency."

Even as a congressman, Mr Cheney's loyalties lay with the White House. According to Congressional Quarterly, in 1981, 83 per cent of his votes backed Ronald Reagan, and in 1982, it was 87 per cent, making him the second strongest supporter in the House. His instincts were reinforced by Iran-Contra. The scandal was caused in part by Reagan's efforts to get around a congressional prohibition on giving aid to the Nicaraguan Contras by using the proceeds of secret arms sales to Iran. Gary Schmitt of the American Enterprise Institute, a conservative think-tank, says Mr Cheney's role as minority chair of the Iran-Contra committee crystallised his views. "The minority report is a sophisticated analysis of the separation of powers and Dick Cheney's staff wrote that section."

One conclusion of the minority report, published in 1987, was that Iran-Contra could be traced to a boundless view of congressional power in the 1970s, and the "state of political guerilla warfare over foreign policy between the legislative and executive branches."