The conservative ascendancy in American politics is coming to an end. For three decades, the right has dominated, with the Republicans winning five of the seven presidential elections since 1980. Conservatives did more than just win elections: even when liberals gained power, they governed on conservative terms.

What were the most important accomplishments of the Clinton presidency? Balancing the budget, welfare reform and the expansion of NATO—not exactly left-of-centre projects. And of Jimmy Carter’s? The deregulation of the airline and natural gas industries.

Neither president set out to accomplish these goals. Indeed, they often resisted them. In the end they had to accept the limits of the possible—just as Republican presidents Dwight Eisenhower and Richard Nixon accepted the limits of the possible in the liberal era from 1930 to 1975.

Neither Mr Clinton nor Mr Carter created a single, major, permanent new national social programme. Mr Clinton failed to bequeath power to his chosen successor; Mr Carter failed even to win a second term.

John Mitchell, Richard Nixon’s attorney-general, predicted in 1970: “This country is going so far right you won’t recognise it.” His prophecy was vindicated. Now its time is up: 2008 is shaping up to be the first decisive Democratic victory since 1964—a 1980 in reverse. The signs are gathering everywhere. Three-quarters of Americans now describe the country as “on the wrong track”. Almost 90 per cent express strong dissatisfaction with the costly healthcare system.

In primaries and caucuses, Democratic contests have drawn more voters than Republican ones. An early estimate after Super Tuesday suggests that, thus far, 11m Americans have cast ballots for Republican candidates, while more than 15m have voted for Democratic ones. Democrats outpolled Republicans by 20 per cent even in the state of South Carolina, maybe the most conservative in the nation.

Usually pundits expect that the party that chooses its nominee first will win the election. That will probably not be true this time. Although the Hillary Clinton-Barack Obama contest looks likely to continue longer than John McCain’s march to the Republican nomination, Democrats tell pollsters they like both candidates—they are just deciding which they like best. Republicans remain divided, with Mr McCain, Mitt Romney and Mike Huckabee each passionately disliked by opposing factions within their party.

In polls, Americans express preference for Democrats over Republicans on almost every issue surveyed, including such traditional Republican advantages as taxes, ethics and competence.

In 2002, equal numbers of Americans identified as Republicans and Democrats. In the six years since, Republican identification has collapsed back to the level recorded before Ronald Reagan. The decline has been steepest among young voters. If they eat right, exercise and wear seatbelts, today’s 20-somethings will be voting against George W. Bush deep into the 2060s. Most ominously, US polls show an ideological sea change: a desire for a more activist government, a loss of interest in the tax question and a shift to the left on most social issues (although not, interestingly, abortion).

As things are going, the Democratic nominee will win a majority of the votes cast (unlike Mr Clinton). They will almost certainly gain an increased majority in Congress (unlike Mr Carter). If the present mood lasts, that nominee will have a green light to move the US in new policy directions (unlike either Mr Clinton or Mr Carter).

The stage has been set for the boldest and most dramatic redirection of US politics since Reagan’s first year in office. Of course, there are no guarantees in politics. An inept president could bungle his or her chances. Unexpected events could intrude: a nuclear test in Iran, a major terrorist attack on US soil or some attention-grabbing political scandal. But given moderate luck and skill, the next president could join Reagan, Lyndon Johnson and Franklin Roosevelt as one of the grand reshapers of politics and government.

Tragically, that reshaping is likely to be for the worse. The things that Mrs Clinton and Mr Obama want to do are likely to prove costly and counterproductive, if not outright disastrous. A greater government role in healthcare, higher taxes, tighter regulation, more social welfare, an increased flow of low-skilled migrants with amnesty for those already here, a cut-and-run from Iraq: these are not measures likely to improve US competitiveness or enhance America’s standing in the world.

To prevent these negative consequences—to retrieve victory from impending defeat—would require more creativity and responsiveness than Republicans and conservatives have displayed for many years. Unless American conservatism can rejuvenate itself, the odds favour the liberal left holding sway until the day that its own errors and delusions lay it low again.