Three months ago, a poll by the same organisation showed Democrats leading Republicans by 52 to 40 per cent, fuelling Democrats' hopes that they could win back the House of Representatives in November. That gap has narrowed to 46 to 44 - regarded as statistically insignificant as it falls within the poll's 3.5 per cent margin of error.
One factor thought to have contributed to the Democrats' decline is a fall in President Clinton's popularity, from 65 per cent in March to 59 per cent now. Pollsters have identified Mr Clinton's personal standing as a crucial indicator at a time when public interest in politics generally is assessed to be low.
No one, either in the most optimistic ranks of the Democratic Party or among the most pessimistic of the Republicans, has any thought that the Democrats could win back the Senate from Republican control. At least 10 seats would need to change hands, and projections give the Democrats at best two. Both parties have, however, allowed themselves to think that the Democrats have a chance of recapturing the 11 seats they would need to win back the 435-member House of Representatives. A total of 59 seats are up for election.
Until the latest poll, the tide was seen to be running strongly in the Democrats' favour - strongly enough to panic the Republicans, if not to give the Democrats more than a flicker of hope that they could win control of the House. The Democrats were seen to have benefited from the strength of the US economy, with Mr Clinton reaping most of the credit and the majority Republicans blamed for the non-passage of popular legislation - above all, restrictions on the tobacco companies.
Before the last mid-term elections four years ago, the economy was cited as the main concern by two thirds of the electorate and the Republicans won their landslide victory on Newt Gingrich's Contract with America. Now, barely one quarter of voters say they are worried about the economy.
Demography also seems to be on the Democrats' side, with women of voting age outnumbering men by 7 million, and a sharp rise in the number of Hispanics qualified to vote. Both groups tend to favour the Democrats, although their voting preference is counterbalanced by their greater tendency not to vote at all.
According to Norman Ornstein, an influential analyst on the political right, America could be described as being "a hotbed of social rest", with the economy flourishing, crime falling and a President in the White House whose personal popularity rivals that of Dwight Eisenhower and Ronald Reagan at their peak.
Against this, however, are incumbency, history - and the unexpected, all of which work for the Republicans. The fact that so many Americans are feeling good about themselves and the state of the country is said to favour incumbents - at state and national level. Most state governors seeking re-election in November are expected to be returned. The US Congress, for the first time since 1974, has a positive approval rating, a change which makes the Democrats' quest to win the House even more of a struggle.
Historically, the party of the sitting President loses in mid-term Congressional elections, and has tended to lose more heavily in the sixth year of a presidency. Mr Clinton's personal popularity appeared to make this less likely in 1998, but no one rules out some development on the sex-scandal front that could cause a precipitate fall in his ratings, with a knock- on effect on the standing of the party and the fortunes of Democratic candidates at the polls.
The chances of Vice-President Al Gore winning the Democrat nomination, and the Presidency, for the Democrats in 2000 are judged to be greater if he has a Republican-majority Congress that he can blame for obstruction than if there is a hybrid Congress that has still achieved nothing.Reuse content