The first thing you are taught in a politics degree is that power is by nature ever-shifting; you can have stride the world one moment and have your power disappear into the ether the next. So it is with American politics.

Less than two years ago, Obama was seemingly invincible. Elected by a massive landslide in a flush of national euphoria, it seemed as if he were better placed than any of his predecessors to enact real and lasting change. What many people forget, however, is that the US Presidency was never really intended to be a particularly powerful position. The President was originally intended to conduct America’s foreign affairs and lead the military, while Congress would get on with dealing with domestic policy. A President is only powerful domestically when he can get Congress on side, which is difficult at the best of times, even when – as has been the case since 2008 – the President and both the House and the Senate have been of the same party. The pivotal role of Congress would partly explain both why Obama has had such a difficult start to his time in office and why next week’s elections are so crucial for the President himself and for the country.

Next Tuesday, voters will elect 37 of 100 Senators, all 435 Members of the House of Representatives, 36 of 50 State Governors, state-level representatives in 46 states and a whole range of state offices, right from local school boards and railroad commissioners to state treasurers and, infamously, "dogcatchers" – town officials tasked with the responsibility to round up stray dogs. US voters are also empowered to vote on various legislative changes; Coloradans will be asked whether they want to amend their state constitution so that foetuses have a right to life, while people across California will vote to make the posession of Cannabis legal.

Tuesday night will be a bad one for the Democrats. Their 59-41 advantage in the Senate will be cut down something much narrower as a whole generation of long-serving incumbent Democrat Senators like Arkansas’ Blanche Lincoln and Wisconsin’s Russ Feingold look certain to lose their seats. The Democrats will have to take refuge in the Senate and White House as their majority in the House will be wiped out and as the Republicans increase their number of state Governors. The Conservative right’s bête noire, House Speaker Nancy Pelosi will lose the job she has held for four years, setting up a showdown between Obama and new Speaker John Boehner, which is likely to be reminiscent of the five-year-long mammoth struggle between Clinton and his Republican Speaker, Newt Gingrich. At the state level, the Republicans will win walk into another seven Governors’ mansions, and pick up more than 400 state legislature seats, resulting in around 10 state Senate and House seats going to the party.

There is something more than the usual first-term blues at play here. Taking 1946 as a starting point, the average mid-term losses for a President are three Senate seats and 25 seats in the House, with the 2010 predictions currently standing at eight losses in the Senate and 45 in the House. This is almost as many as Bill Clinton’s historic loss of 54 seats in 1994.

Incumbency is often an advantage in US politics. An incumbent is able to develop the name recognition that is so important in winning over an electorate which is far less attached to individual parties than is the case with UK voters. Incumbents also tend to attract far more money and can spend their time in office using the chaotic to direct federal spending (known as "Pork") to their district or state to build the latest library, airport or highway for their grateful constituents. This time, however, incumbency is a poisoned chalice for large numbers of Democrats. An electorate angry with the state of the economy is punishing mainly Democratic incumbents. As in the UK, voters are angry that billions of dollars have been spent bailing out banks and large financial institutions while small "mom and pop" businesses have been allowed to go bust, leaving 9% unemployed, the highest rate for many years.

Obama is caught between two increasingly polarized camps: Democrats who are disillusioned with the lack of progress made on key issues and the watering down of health care reform on the one hand, and on the other, fiscal conservatives alarmed at the amount of spending the federal government has engaged in. As ever, small-government Republicans traditionally supportive of the autonomy of the individual states accuse Obama of a "Washington power grab", with "Obamacare" and other fedearal programmes supposedly curtailing states’ rights. Unusually, the "culture wars" of the late 1990s and the Bush era appear to have faded away somewhat, with the fiscal and economic debate pushing out arguments over social and moral issues, like abortion, gay marriage and positive descrimination.

Perhaps the defining feature of this election has been the rise of the "Tea Party". An informal grassroots faction within the Republican party, it grew rapidly throughout 2009, first starting in New York in response to a series of tax rises issued by the state government. Informally led by the 2008 Republican Vice Presidential candidate Sarah Palin, it emphasises the need for low taxes, the reduction of wasteful spending and the national debt, states’ rights, reduction in the size of government and adherence to the fundamentals of the US constitution.

The precise impact on the eventual result is difficult to judge. The Republicans are likely to benefit from the increased enthusiasm of a core segment of its base and an influx of newly-politicized activists, but the "Tea Party" candidates who have won Republican nomination races are likely to ward off prized independent voters and throw to the Democrats races they would otherwise have won. Except for Nevada’s Sharron Angle – who stands is locked in a close race with Senate Majority Leader Harry Reid (effectively the mst important Democrat after Obama) – "Tea Party" candidates are likely to be rejected by the voters next week. The Republicans were looking forward to an easy win in the usually Democratic state of Delaware until novice candidate Christine O’Donnell won the nomination fight there. Since then, it has been revealed that she claimed to have dabbled in witchcraft and in a debate last week, appeared not to know the content of the constitution, including many of its key Bill of Rights amendments. Democrat Chris Coons, trailing up to that point, is now looking forward to an unexpectedly easy win. Some commentators have even suggested that without the "Tea Party", the Republicans would have been in a position to win the Senate as well as the House.

The victories of more extreme Republicans has pushed many ousted moderate incumbents to run as independents, creating interesting three-way races. Having lost to the "Tea Party" ’s Joe Miller, Alaska Senator Lisa Murkowski is using an electoral law that allows voters to "write-in" their preferred candidate even if they not on the ballot in an attempt to keep hold of her job. Florida Governor Charlie Crist, having lost out on his party’s nomination for his state’s Senate seat, is running as an Independent against the charismatic conservative, Marco Rubio.

The impact on the next Presidential election is yet to be seen. Clinton went on to win the 1996 election despite being ovewhelmingly rejected two years previously and was more successful in his second term than his first. What is clear though, is that we are heading for a much more closely and bitterly contested politics than has been the case in the past. Obama may well survive, but the spirit of 2008 seems to have gone forever.