WASHINGTON, DC • As United States Republicans and Democrats go through the long process of selecting a nominee for next year's presidential election, both parties face the same question: Will the anti-establishment - even anti-political - mood now dominating the contest last?
For once, Labour Day (the first Monday in September) was not the presidential race's demarcation point: The overall themes had already been set. Revulsion at government and traditional politicians hit the contest like a tornado in the summer, flattening the campaigns of some who were once seen as serious contenders.
Among Republicans, this sentiment is of course no surprise, given their party's steady rightward drift and consistent antipathy towards President Barack Obama. But it suited a wealthy, noisy braggart who barrelled into the race attacking conventional politicians as "stupid" and insisting that he alone could get things done.
Those who wrote off Mr Donald Trump as a "buffoon" failed to see that he has shrewdly read the Republican zeitgeist, and that he knows precisely where to stick the knife into competitors. His depiction of former Florida governor Jeb Bush as a man of "low energy" has done real damage to a candidate whom many had assumed would be the favourite.
"The Donald" (no one has better name recognition than the former TV personality) has pitched his appeal both to US patriotism and the country's dark side. His slogan, "Make America Great Again", is aimed at those who are frustrated that the US can no longer impose its will on an increasingly confusing world. For them, and for Mr Trump, Mr Obama is to blame: He does not stand up to foreign leaders; he withdrew from Iraq too soon; he even "apologises" for America.
Mr Trump plays to America's persistent veins of racism and nativism: He vows somehow to round up and deport some 11 million undocumented aliens and fortify the US border with Mexico by building a wall - paid for by Mexico. His striking narcissism is both his trademark and his policy.
Around the middle of last month, as Mr Trump's poll numbers rose even after public statements that would have brought down mere mortal candidates, it dawned on the pundits that he was no summer infatuation. It became evident that he might win the first nominating contest, the Iowa caucuses, and that he was leading in the second, New Hampshire, and other states. It was no longer laughable to say he could be the Republican nominee.
But the "anti-system" mood of this election campaign is not confined to the Republicans. Mr Bernie Sanders the socialist and Mr Trump the plutocrat are addressing much the same impulse. Speaking in clear, declarative sentences, Mr Sanders sets forth an idealistic conception of government policy that appeals to many on the growing left of the Democratic Party.
By contrast, Mr Bush and the Democrats' presumed nominee, Mrs Hillary Clinton, embody traditional politics. Both come across as focus-grouped, packaged and cautious, whereas Mr Trump and Mr Sanders are seen by their followers as "telling it like it is".
Mr Sanders appeals to the popular frustration with the compromises made by America's leaders, including the centrist Bill Clinton. Mrs Clinton, trying to straddle the divide between the two wings of the Democratic Party, is increasingly leaning to the left as Mr Sanders draws huge crowds, something she has yet to achieve.
Meanwhile, Mr Trump's appeal among Republicans is across the board: moderates and conservatives, college-educated, evangelicals, men and women. His closest Republican rival, Mr Ben Carson, a renowned neurosurgeon, also has no political experience and says outlandish things. But Mr Carson says them quietly, which may be why his favourability rating in Iowa is higher than that of his Republican competitors.
Mr Trump and Mr Carson, along with two other candidates running as political outsiders - Mr Ted Cruz, a senator from Texas, and former Hewlett-Packard CEO Carly Fiorina - account for around 60 per cent of support among Iowa Republicans. Mr Bush and the rest of the field, including Mr Rand Paul, Mr Scott Walker and Mr Marco Rubio - all one-time darlings of the political press - are floundering. To recover ground, some, especially Mr Walker, have fallen into the trap of trying to out-trump Mr Trump.
But there is only one Trump, and his candidacy is causing conniptions on the part of party officials, particularly given his campaign's open hostility towards Latinos. Following Mr Obama's re-election, in 2012, Republican leaders commissioned a study that showed the party's nominee will have to win more Latino votes than ever to win the White House. There is scant chance of that if Mr Trump is the party's standard-bearer.
So far, Mr Trump has defied the laws of political gravity. But it remains possible that his candidacy will crash as some of his rivals drop out and leave their supporters to crystallise around someone they see as a more viable alternative. That would be a relief to party leaders, who recently obtained Mr Trump's vow not to mount an independent campaign should he fail to win the party's nomination.
In the meantime, both party establishments have reason to be nervous. With Mr Sanders polling well ahead of Mrs Clinton in New Hampshire, serious commentators have begun speculating that Americans will ultimately be asked to choose between Mr Sanders and Mr Trump.
• The writer is the author, most recently, of Washington Journal: Reporting Watergate And Richard Nixon's Downfall.