Mardi Gras in New Orleans has always had a gothic element. The voodoo culture dates from the African American diaspora, though it’s now mostly for tourists. But this year there was an authentically macabre dimension to Fat Tuesday.

One of the main arteries of the city, Canal Street, has been blocked since a multi-storey hotel building collapsed in October. Three bodies remain in the rubble, only partially covered.

Walking to the famous French Quarter two blocks away you are accosted by hucksters offering to take you on body-sighting tours of the devastation.

There could be no more potent metaphor for the condition of urban America. It’s in a state of collapse and no-one wants to take responsibility.

The dead construction workers were Latinos, and there is a widespread suspicion that this could never have happened had they been white.

Yet, the mayor of New Orleans, LaToya Cantrell, is black. If this is about racial discrimination then it’s not as we know it.

Say what you like about the state of public administration in Scotland – the problems with our hospitals and the potholes in our roads – but if bodies had been left unburied on a building site for four months in Glasgow there would have been consequences.

Something has gone terribly wrong in America, as the wealth gap widens and people lose faith in democratic politics. A fish rots from the head, as they say here. America isn’t working because it has a self-indulgent and irresponsible president in Donald Trump.

People are now worrying about the consequences of a coronavirus pandemic. With Trump in charge, one is inclined to fear the worst.

The US political system used to be admired across the world. Tony Blair and Gordon Brown were infatuated and tried to remake Labour in the image of Bill Clinton’s Democratic Party. But he is discredited and the Democratic Party is also in a bad way.

Next week, on Super Tuesday, a raft of 14 state primaries register their verdicts on the contenders for the Democratic presidential nomination. Who comes out on top will almost certainly take on Donald Trump in November.

But Democrats are in near despair because none of their geriatric frontrunners looks in any shape to take on The Donald.

Bernie Sanders, a 78-year-old democratic socialist, goes into Super Tuesday the favourite, despite his getting a drubbing from his rivals in South Carolina last week. He’s fought a good fight and has legions of loyal, mostly young, activists.

But he had a heart attack earlier this year and doesn’t have the confidence of the Democratic Party Establishment. They think that the US is not ready for free university tuition and universal healthcare.

Sanders carries a lot of baggage too. Such as his favourable remarks about the Cuban dictator, Fidel Castro. Ominously, he is Trump’s favourite candidate.

Sanders is faced by another 78-year-old. Multi-billionaire Mike Bloomberg, a former New York mayor, is trying flagrantly to buy the Democratic nomination. He has already spent nearly half-a-billion on campaign materials and TV ads, mostly attacking his Democratic Party rivals.

He is hated by left-wing Democrats, the “Bernie bros”. But there are many in the party quietly thinking that Bloomberg’s vast wealth may be their only hope against Trump.

“It takes a billionaire,” said one supporter paraphrasing Hillary Clinton’s book It Takes A Village.

In theory, 77-year-old Joe Biden, Barack Obama’s vice-president, should do well on Super Tuesday. But his campaign has been faltering. He has been awkward in recent TV debates and looks to have run out of steam.

So has 71-year-old former teacher Elizabeth Warren. She is highly regarded in the Democratic Party, but middle America seems unpersuaded by her feminism.

Intersectional politics may go down well on Twitter but not in the bayous of Louisiana.

The baby of the race at 38, Pete Buttigieg (pronounced “boot edge edge”), has a lot of support from none-of-the-above primary voters, but it hasn’t shown through.

He is the kind of well-spoken and telegenic candidate who might have done well in the days when the press and mainstream media still dominated political coverage.

Buttigieg, who is openly gay, has the wit and fluency of a latter-day Bill Clinton. But even being articulate has become a handicap. Mayor Pete’s rivals mock him for parroting lines from The West Wing.

This has come down to a contest between grizzled old bears. Bloomberg oozes privilege and a sinister complacency. Sanders sounds perpetually bad-tempered and pugnacious.

There’s a lot to be cross about in America. In many ways, Sanders is a breath of fresh air, a genuine force for change. His agenda echoes Jeremy’s Corbyn’s: wealth tax, Green New Deal, Medicare for all.

“Yeah, and look what happened to Corbyn,” say mainstream Democratic Party pundits, who believe America is never going to “feel the Bern”.

In a quintessentially capitalist country, Sanders is campaigning for what many Americans regard as socialism or even communism

His universal healthcare policy may seem uncontentious in the UK, where the NHS is sacrosanct. But in racially divided America it is hugely problematic.

White Americans, with their own expensive healthcare plans, don’t want to pay for “psychos, illegals, welfare cheats and drug dealers”, as one American put it to me in a Bay St Louis bar. This is really a euphemism for blacks, Hispanics and illegal immigrants.

The US pays twice as much for a health service that leaves 33 million Americans without cover. But mention the NHS here and many will shake their heads: “you get what you pay for”. End of story.

The Democrats are right to be worried. Trump is arguably the worst president in American history. His belligerence, climate denialism and trade wars have made the United States an international pariah.

Yet the Dems have no-one who looks capable of defeating him. This lamentable state of affairs arises in part because the left never really understood the Trump phenomenon.

They preferred to believe that Trump never really won in 2016. That he only got to the White House because of Russian interference, digital manipulation and/or bribery.

But many Americans remain intensely religious and their patriotism is ingrained in a way we can barely comprehend. Mardi Gras parades are often led by dress marines – and they get the biggest cheers. People wanted to Make America Great Again.

Yet walking down Canal Street, America is not so great. It’s hard to understand why the left seems unable to take on a president whose signature policy has been tax cuts for the rich. The place is on the edge. Opioid casualties lie on the streets ignored by passers-by. Americans with obvious health problems hang around McDonald’s begging for a dollar.

As the American writer Michael Lind explains in his book The New Class War, voting for populists like Trump represents “cries of rage” from many lower class Americans, who feel that the intellectual left regard them as a “basket of deplorables”.

Mike Bloomberg has not been doing well in the pre-Super Tuesday opinion polls. But cynical Democrats still hope his money might succeed where Bernie fails.