Tuesday's midterm elections were, depending on your viewpoint, either an historic turning point reversing a long era of Republican ascendancy or just another of those periodic revolts by voters against the party in power that has no long-term significance.

Democrats, unsurprisingly, favour the epochal interpretation. Their leaders have plenty of reasons for the hyperbole. The party gained more seats than in any election since the midterms after Richard Nixon’s Watergate resignation in 1974. On only three other occasions in the last century — 1932, 1952 and 1994 — has either party taken over House and Senate at a single election. Only one of those wins — the Republicans in 1994 — came in midterm elections.

And though the scale of the Democrats’ victory this week was smaller than that of the Republicans in 1994 in simple numerical terms, it was almost as impressive. Gerrymandering of congressional districts means there are far fewer House of Representative seats genuinely up for grabs than was the case 12 years ago. In the Senate the Democrats not only look to have gained six of the seven seats that were considered at all winnable — they also knocked off usually hard-to-beat incumbents in every one. They didn’t lose a single seat of their own — House, Senate or Governors’ races.

They now enjoy a bigger majority in the House of Representatives than the Republicans have had at any time in the 12 years in which they have been in control.

All of which supports the case that this was a landmark election. It calls to mind similar midterm earthquakes: 1958, when Dwight Eisenhower’s Republicans lost dozens of seats and ushered in an era of Democratic dominance; 1966, in the middle of the Vietnam War, which began the recovery of the Republican party; 1974, the Watergate election that produced the Jimmy Carter presidency; and, of course, the 1994 Republican revolution itself.

But Republicans — or some of them — can point to similarly compelling historical evidence that Tuesday was, in the great scheme of things, no big deal. Historically, the congressional elections in the sixth year of a party’s occupancy of the White House are usually horrible for the incumbent’s allies. Over the past century, in these elections, the president’s party has lost an average of 32 seats in the House and six in the Senate. Guess what? The Democrats seem to have gained about 32 seats in the House and six in the Senate.

In the past these six-year itches have not necessarily led to devastating losses for the party in subsequent elections. What’s more, the largest midterm setback in the past 30 years, in Bill Clinton’s first term in 1994, was followed two years later by Mr Clinton’s easy re-election.

Further, Republicans argue, in 2006 they were fighting extraordinary headwinds. An unpopular president, a failing war and a host of congressional scandals all reinforced voters’ call for a change.

So what’s the truth? Paradigm shift or protest vote? The exit polls offer help to the Republicans. They suggest the election was in large part a vote against President Bush and the scandal-torn congressional leadership. Both of those will be taken care of. Mr Bush is not running again and congressional Republicans will be getting used to subdued opposition for a while.

If it’s sensible, the party will find some way out of the Iraq morass. Then it can look forward to a string of attractive potential candidates for the 2008 presidential contest, who look, at this stage, more electable than Hillary Clinton or any of her opponents on the Democratic side.

And yet. Three factors in the 2006 election should give Republicans pause.

First, their dominance on national security — the key to their electoral success for the past 30 years — has been badly impaired by the Iraq war. Exit polls said voters favoured Democrats not only on traditional issues such as the economy and health care, but also on handling Iraq. If the war continues to spiral into disaster it could set back the Republican reputation for national security competence by a generation.

Secondly, Democrats have learnt their lesson from the past painful decade. They fielded attractive, socially moderate candidates who emphasised their religious convictions and played down issues such as abortion or gun control. They even looked like a new breed of Democrats, more in touch with middle America.

Thirdly the Democrats were the beneficiaries on Tuesday of some significant long- term social and demographic changes that might just point to a turning of the tide in American politics. Democratic candidates performed unusually well in the most rapidly growing parts of America.

Their breakthrough marks the certain halt — at least for now — of the long Republican march of the past decade.

But it also carried with it the outlines of a route map with which Democrats now hope to lead the country in another direction.

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