Democrats struggle against supercharged Republican voters
Less than two years ago, Democrats basked in the glow of their most impressive political triumph in more than four decades.
Today, they are contemplating the very real prospect that they could lose their House majority and possibly, though less plausibly, control of the Senate as well in four weeks' time.
An economy stuck in neutral and a jobless rate that remains stubbornly high. Growing criticism of the federal government, fuelled in part by opposition to President Barack Obama's own signature programmes - last year's economic stimulus and this year's healthcare overhaul. And finally, continued frustration with the political status quo, which is now directed at Democrats.
Next month's mid-term is shaping up as a classic "wave" election - one in which national trends endanger the party in power.
The Republicans lost control of Congress in the 2006 wave, which was powered by opposition to the war in Iraq and dissatisfaction with President George W Bush.
Just 12 years earlier, an electoral wave wiped out the Democrats, costing them their 40-year hold on the House and control of the Senate.
Just as in 2006 and 1994, this year it is the political opposition that has greater energy and enthusiasm. In the most recent Pew Research Center survey, 83% of Republican voters said they will definitely vote, compared with 69% of Democratic voters.
The Republican Party's lead on this measure is the highest for either party at this stage in the last four mid-term campaigns.
Today, Republicans are benefiting from the intensity brought by supporters of the Tea Party movement, the anti-government insurgency that exploded on to the political scene last year.
The Tea Party has been a mixed blessing for Republicans. Even some party leaders believe, for instance, that the movement's support of Christine O'Donnell could cost the party an opportunity to pick up the Delaware Senate seat once held by Vice President Joe Biden.
Yet there is also no doubt that the Tea Party has been instrumental in boosting the Republican Party's turnout advantage - fully 88% of Republican voters who agree with the Tea Party say they will definitely vote, compared with just 66% of Republican voters who are unaware of the movement or have no opinion of it.
Another major factor that has jeopardised Democrats' control of Congress is their loss of support among political independents and other non-partisan voters.
Just two years ago, independents - who make up a larger share of the electorate than either Democrats or Republicans - backed Obama over John McCain by eight points. And in 2006, when Democrats won control of Congress, independent voters favoured Democratic candidates by 18 points over their Republican rivals.
But this year, independents support Republican candidates by 49% to 36% - a staggering 31-point swing from four years ago.
Since 2006, independents have become somewhat more conservative and less trusting of the federal government.
But the independents' movement toward the Republican Party has more to do with changing views of the parties' performance than with changes in ideology. And these evaluations help explain why independents have soured on the Democrats: 42% now say the Republican Party can do a better job of managing the government while 31% favor the Democrats.
In 2006, Democrats led by an almost identical margin - 38% to 26% - as better able to manage the government.
Despite the promising signs for Republicans, there is little evidence that the party's "brand" has improved.
In fact, favourable ratings for the Republican Party have shown little overall improvement over the past four years.
And while favourable ratings for the Democratic Party have tumbled since Obama took office, the party is still viewed somewhat more positively than the Republican Party.
Yet the fundamental dynamics of this year's election are unlikely to change over the next four weeks.
It seems likely that Republicans will make substantial gains on 2 November. What is not certain is whether they will achieve a net gain of 39 seats needed to claim a majority in the House, or the 10 seats needed to win a Senate majority.
For Democrats to hang on to their majorities, they will need to narrow the Republicans' turnout advantage by increasing engagement among the same groups of voters who were among Obama's strongest supporters in 2008, notably minorities and young people. This may explain why Obama travelled to Wisconsin, a swing state, last week for a get-out-the-vote rally on a university campus.
Both Mr Obama and Mr Biden have recently complained about the lack of enthusiasm among Democratic voters.
However, the Democratic base is not noticeably less inclined to vote than is typically the case during congressional elections. It is the opposition's enthusiasm - not their own side's lethargy - that is their party's biggest problem in this election.