On the right of the spectrum, the populist Tea Party movement has emerged. Its strident rhetoric has infected all ranks of the Republican Party.
This reached a dismal zenith when Tea Party-led conservatives in the Republican-controlled House of Representatives held the creditworthiness of the US to ransom over the hitherto mundane issue of an increase in the national debt ceiling.
The Tea Party's unofficial leaders, Sarah Palin and Michele Bachmann, have quickly had their weaknesses exposed. Palin was astute enough not to put herself forward for nomination, and Bachmann's campaign quickly faltered. But other Republican candidates have felt it necessary to adopt some of their zealotry. Slashing spending, a downsized government and unwillingness to raise taxes are themes even of moderate Republicans such as Mitt Romney.
Mr Romney should be the clear front-runner. If he is wooden in much of his demeanour and far from convincing, he at least has the qualifications for the job.
It says much about the state of the Republicans, and of the country, that several other candidates with poorer credentials have achieved high profiles, if only for a short time.
The latest of these is Herman Cain, who is now having to fight off allegations of sexual harassment. It remains possible that the Republican nomination race will still throw up a candidate who inspires the disaffected and does not have a history of, or a propensity for, gaffes.
The Republicans' refusal to to make compromises with President Obama - in a political system that requires members of Congress to reach across the aisle - has strengthened the Democrats' liberal wing.
The confrontational tactics and angry atmosphere have left little room for those advocating centrist politics.
The President often seems like a beacon of sanity in this environment, but it is, nonetheless, true that his inexperience has been savagely exposed. Many of those who supported him have become demoralised or disenchanted.
President Obama's approval ratings hover between 40 and 45 per cent. That is not the stuff of comfortable re-election, although Ronald Reagan rebounded from that point in 1984. It may be telling that Americans have a dramatically lower opinion of Congress than of President Obama. The Republicans could have overplayed their hand in the eyes of independent voters.
But the President cannot blame all the failings of his stewardship on the Republicans' obduracy in Congress. He is particularly vulnerable if the limping economy suffers another reversal. Even the best-case scenarios offer little for most Americans. President Obama will rely heavily on his undoubted campaign skills, and on the hope that no formidable Republican candidate will emerge. Most of all, he will have to offer palliatives for a general mood of disillusionment.