The Watergate scandal not only gave America a nightmarish civics lesson, but brought about far-reaching changes to government, politics and journalism that are being felt still to this day.

The power dynamic between the executive and legislative branches altered radically, as lawmakers on Capitol Hill sought to rein in the 'imperial presidency'. Campaign finance reforms imposed new disciplines on political fundraising. A freedom of information act, passed in spite of Gerald Ford's veto, shone much-needed light on presidential decision-making. The National Emergencies Act in 1976 restricted the power of the president to declare a state of emergency (unbeknown to most US citizens, America had been in an open-ended state of emergency since 1950).

Gavel to gavel television coverage of the Watergate hearings built pressure of US lawmakers to allow cameras into the House and Senate, which started on an experimental basis in 1977. The character of Capitol Hill also changed, as the congressional seniority system was overhauled. A new guard of Democratic lawmakers elected in 1974, following Richard Nixon's resignation, arrived with an insurgent spirit, and were determined not to wait at the back of the queue for plum committee assignments. Dubbed the Watergate Babies, they included Patrick Leahy, Tom Harkin, Henry Waxman, and the former Senator Chris Dodd.

As for journalism, young reporters converged on Washington hoping that they, too, might one day see themselves played on film by Dustin Hoffman or perhaps Robert Redford. Up until the late-1960s, relations between the White House and its press corps had often been ridiculously cosy. Ben Bradlee, the editor of the Washington Post at the time of Watergate, was such a close personal friend of Jack Kennedy that in 1960, while awaiting the first returns on the night of the crucial West Virginia primary, they went to watch a soft porn movie together.

Bob Woodward and Carl Bernstein, who, significantly, were not members of the White House press corps, changed that culture. Post-Watergate, political coverage became much more adversarial, with the fall of a president as the ultimate journalistic scalp. More drearily, the suffix '–gate' soon came to be attached to any scandal, large or small, robbing it of any meaning.

Much more profound is the extent to which Watergate led to the closer marrying of the US political and legal systems. The process continued with the impeachment of Bill Clinton, and reached its zenith at the end of the Florida recount in 2000, when the US Supreme Court, in Bush v Gore, essentially decided the outcome of the race. Post-Watergate, the juridical letter of the constitution has come to crush its spirit. Law has overtaken history as the academic touchstone of politics. Washington, which throughout the 1950s and into the 1960s had a surprisingly collegiate and bipartisan feel, now has a sour, prosecutorial air. Just as politics has become more legalistic and investigative, the US Supreme Court has become more politicised.

Little wonder, then, that the very legitimacy of the last three presidents, Clinton, Bush and Obama, has been challenged. Often, they have been cast by their opponents as crooks, liars and frauds.

Certainly, the imperial presidency is no more, but the changes in the balance of Washington power, and the new checks and balances that have flowed from it, have had an emasculating effect. Much of America's present dysfunction can be traced to the aftermath of 17 June 1972, the night of the break-in at the Democratic National Committee headquarters in a once obscure office complex. Indeed, one of the main effects of that third-rate burglary has been to contribute to a second-rate politics.