For Washington-based analysts, the United States has transformed itself, just this once, into a parliamentary democracy, where the local vote may determine the fate of the national leader. If too many Democrats stay at home, this will be seem as a vote of no confidence in President Clinton; if they come out in force, or even maintain average levels of turnout, that will be seen as a vote of confidence.
If the Republicans make big gains, that will represent not only a moral victory, but a practical one: the composition of congressional committees will reflect their votes and, with President Clinton already the subject of impeachment hearings, the numbers are crucial. In the House of Representatives, all 435 seats are in contention; in the Senate, 34.
In the unlikely event that Republicans increase their number of senators from 55 to 67, they would have the two-thirds majority necessary to impeach the President without Democrat support.
More realistic projections are for Republicans to win another five seats.
How judgements change. This time last year, no one dared even project a national aspect on to these mid-term elections. Analysts in Washington predicted a campaign that would be mainstream and boring, inclined most probably to endorse the status quo.
At the turn of the year, those same analysts predicted that the Democrats had an outside chance of winning the 22 seats they would need to overturn the Republican majority in the House of Representatives. By August, they forecast a Republican landslide in both houses. And now, with barely two weeks to polling day, the only "expert" consensus is that no one dare forecast the result. It is not that the result is too close to call, but that no one wants to hazard a guess about the impact of national scandal on essentially local elections. Suddenly, those boring, mainstream, status- quo mid-terms are being billed the most exciting in a generation.
The chief reason for all the uncertainty is the criss-crossing of two strands: the nation's economic fortunes and Mr Clinton's sex life. Until last month, the prevailing sense of economic well-being was seen as protecting incumbents, and helping Democrats. If the voters were happy, as they appeared to be, why vote for change? Opinion polls showed that satisfaction with Congress as an institution and with individual members was high.
Then in January the Monica Lewinsky affair broke. The Democrats' advantage was gone. By June, President Clinton's personal stock was so low that he looked likely to become an electoral liability to his cash-strapped party.
By last month, though, with confession and contrition well received and his job approval rating in the polls remaining stubbornly high, he looked safe - and so did most Democratic incumbents. But what no one can guarantee is whether, when voters tell pollsters they are unworried about the President's behaviour, they are telling the truth.
The Clinton factor - whether it exists and which way it might push voters - is one imponderable and the other is the economy. The bounding confidence of June has yielded to defensive worry. Recent falls in the Dow Jones Index have subdued people's desire to spend. Will the economic well-being that was supposed to protect Congressional incumbents now expose them instead? Is the downturn too late to affect the voting? Or was the national economy never going to affect the elections anyway?
With so many variables, the pollsters may be forgiven for their reticence. But there is little sign yet that the voters are thinking in national terms. As well as Congressmen, they must elect local officials - judges and school-board members, and no fewer than 36 state governors. There are few signs, either, that the candidates - even those running for national office - want to campaign on national issues. Where candidates have tried to invoke moral values as an election issue, the response has been very mixed.
The only pattern to emerge from this year's campaign is that there is almost no pattern. And if voters remain content to leave aside the Clinton factor, the results could be disparate indeed.
There are not even any striking philosophical differences between the two main parties. Education and law and order come at or near the top of most voters' concerns, according to the latest opinion polls, but the proposed solutions - more money, smaller classes, better teachers, more policing - are similar.
As in Europe, voters have increasingly seemed to favour candidates - especially for local administrative posts such as state governor - who are capable and efficient, rather than of a particular party political persuasion. This shift could help Democratic candidates for governor to prevail over Republican incumbents, but it could also give George W Bush, the son of the former president, a record majority in the race for Texas governor, and a springboard for a presidential bid.
The vote in the South will be scrutinised for what it shows, not just about Mr Clinton's standing, but about the strength of the religious right. Often seen as a fiefdom of the Southern Baptists, the South has been less vehemently critical of Mr Clinton's "inappropriate relationship" with Ms Lewinsky than might have been expected, leading some to venture that the tide may have turned for the influence of Christian fundamentalism in national politics.Reuse content