Image copyright Getty Images Image caption Kennedy, Reagan and Obama all won the White House on expressions of hope... but also outpourings of fear

The romanticised view of US presidential elections is that they present quadrennial opportunities for national renewal; that they are expressions of hope and optimism that reflect this country's founding belief in its inexorable advancement and improvement.

Peered at through rose-coloured spectacles, they become the democratic flowering of American exceptionalism.

Some post-war examples might include John F Kennedy's victory in 1960, which was interpreted as bringing the somnolence of the Eisenhower years to an end and unbridling the frenetic energy of the Sixties.

At the 1980 election, Ronald Reagan is credited with bringing closure to America's long national nightmare of Vietnam and Watergate.

In 2008, Barack Obama seemed to personify how America could renew itself after the destruction of the Twin Towers and the collapse of Lehman Brothers.

On closer examination, however, those elections don't just look like expressions of hope but also outpourings of fear.

Jack Kennedy exploited Cold War anxieties that America was falling behind the Soviet Union, even inventing a "missile gap" that gave Moscow the supposed nuclear edge.

Ronald Reagan kicked off his election campaign by championing "states' rights" in Philadelphia, Mississippi - the site of the "Mississippi Burning" murders in the 1960s - using language that articulated southern white fears about the encroachment of the federal government and advancement of African-Americans in a setting loaded with shadowy symbolism.

Image copyright Getty Images Image caption During the 2008 election campaign, Lehman Brothers filed for the largest bankruptcy in US history

In the aftermath of the financial crisis, Barack Obama profited from anxieties that the American economy was in meltdown.

Deep pool of resentment

All three benefited from what the political theorist Richard Hofstadter memorably described in the mid-1960s as "the paranoid style in American politics".

"American politics has often been an arena for angry minds," wrote Hofstadter, a line penned in 1964 that resonates just as strongly today. Now, as then, American elections commonly witness the triumph of fear over hope.

As we enter election year, there is a deep pool of nervousness and resentment from which to draw.

On the economic front, there is the shrinkage of the American middle class. New figures from Pew Research suggest that for the first time in more than four decades, the middle class is no longer in the majority.

People becoming wealthy enough to be defined as "better off" explain some of this shrinkage. But 20% of Americans are now in the lowest income tier, compared with 16% in the early 1970s.

The median wealth of middle-class households has also seen a dramatic fall over the course of this century, decreasing by 28% from 2001 to 2013. Pew found also that median incomes in all wealth brackets were lower in 2014 than in 2000. The "American dream" is not such an animating force.

What's often called the Uberisation of the economy - the move towards freelancing and flexible working arrangements - is eroding the traditional compact between employer and employee.

Terror fears

Fears about economic security overlap with fears about national security.

In the aftermath of the San Bernardino and Paris attacks, Americans are more fearful about the prospect of terrorist attacks than at any time since 9/11, according to a poll conducted by the New York Times and CBS News.

Some 44% of the public thought an attack was "very" likely in the next few months. A poll this month from Gallup suggested that Americans regard terrorism as the country's number one problem.

Confidence in American institutions has also been on the wane, as seen in another Gallup poll. Here are the results for how many people said they had a "great deal of confidence" in the following:

Congress 4%

the White House 16%

the Supreme Court 14%

public schools 12%

banks 12%

organised labour 12%

the criminal justice system 9%

big business 9%

newspapers 10%

television news 10%

These are not good days for the American establishment, whose pillars look increasingly wobbly.

Gun control debate

Beyond these statistics lies further evidence of national anxiety.

The spate of mass shootings - almost one a day in 2015 - has not just spread fears about public safety, but seemingly heightened concerns among gun owners that the federal government will some day restrict the availability of firearms (not that gun control is going anywhere in Congress).

That offers one explanation for the spike in gun sales on Black Friday in November, when the FBI ran a record-breaking 185,345 background checks, about two per second.

US gun crime in 2015 Figures up to 3 December 353 Mass shootings 62 shootings at schools

12,223 people killed in gun incidents

24,722 people injured in gun incidents AP

The Black Lives Matter campaign continues to highlight the brutal excesses of certain police officers. In recent months, a number of leading American university campuses, including Yale, have been restless. Even American football, the national winter sport, seems to be in a perpetual state of scandal.

Populism flourishing

Add to that the unchecked rise of China, the difficulty in combating the group calling itself Islamic State, the inability to humble Vladimir Putin, the failure to defeat the Taliban and a nagging sense of the waning of American international influence and that pool of resentment increasingly resembles a toxic swamp.

The state of the union is perturbed and anxious. America is beset by a climate of uncertainty and fear in which populist campaigns, like those mounted by Donald Trump on the right and Bernie Sanders on the left, can flourish.

Image copyright Reuters/AP Image caption Donald Trump is the Republican frontrunner, while Democrat Bernie Sanders trails Hillary Clinton in the polls

Worryingly for Hillary Clinton, periods of national anxiety also have a tendency of producing party change in the White House. One thinks of Jack Kennedy in 1960, Richard Nixon in 1968, Jimmy Carter in 1976, Ronald Reagan in 1980 and Bill Clinton in 1992.

Back then, Bill Clinton cast himself as the candidate who still believed "in a place called Hope", his birthplace, but his success stemmed from enunciating the economic apprehensions of "the forgotten middle class".

For all the demographic and electoral map advantages that the Democrats have come to enjoy in presidential politics, Hillary Clinton will also need to give voice to middle class anxieties about stagnant incomes, wealth inequality and dwindling opportunity. It explains the tweet that launched her campaign back in April: "Everyday Americans need a champion, and I want to be that champion."

Whoever ends up on top, the campaign will provide yet more evidence of the paranoid style in American politics. It will not be marked by a sense of national renewal or sunniness.

Rather, 2016 looks set to be a year of fear.