Donald Trump is leading his nearest rival, Ted Cruz, by a massive 42% to 20% in the latest poll from South Carolina, where the second primary takes place tomorrow. The other Republican contenders are trailing behind .  Hillary Clinton, on the other hand seems to be, for the moment, overturning Bernie Sanders’ victory in New Hampshire.

Clinton has the support of 59% of likely Democratic primary voters in South Carolina, which is a lead that has narrowed slightly from last month, according to CBS and reported in Time magazine. The former Secretary of State’s voter base consists largely of black voters, while Sanders, who leads among white voters and young voters, is behind Clinton with 40%, the poll shows.

What is happening? According to Simon Heffer in last Saturday’s London Daily Telegraph , it is all Barak Obama’s fault. In words I would not like to report directly he puts it this way.

Since George HW Bush left office in 1993 America has been ruled by a spin-obsessed Lothario, a dangerous halfwit and a clever incompetent. They all bore the imprimatur of their respective party machines. For much of America, Barack Obama is the last straw. He is the creator of Donald Trump and Bernie Sanders. If one of them becomes president – and I wouldn’t rule it out – and the world doesn’t like it, they know whom to blame.

Heffer looked back to the high emotions which were running riot across America in November 2008 when the news of Obama’s victory was spreading. They ranged from the barely concealed sourness and anger evident on Fox News to the state of almost convulsive ecstasy gripping the avowedly liberal network, MSNBC.

For many a miracle-worker had arrived in the White House. One inspired cartoonist had drawn a picture of the building and its pond on the front lawn. At the edge of the pond was a conspicuous sign, ‘Please do not walk on the water’.

One of the TV channels interviewed a woman outside her run-down house. She was in tears while telling the interviewer what the victory meant for her. “I now know,” she sobbed, “that my house won’t be foreclosed on.” Heffer hoped she was right, but still had to conclude that the evidence of the seven years since Obama the miracle-worker took office suggests she may have been disappointed.

I had seen Obama at the primaries, Heffer wrote, and at the Democrat Convention. I had waited for him to speak intelligently about the state of America and how he would put it right, but I waited in vain. The cliché at the time, which became more relevant later, was about how he campaigned in poetry but would govern in prose. Some prose can be magnificent: but not his.

He admits that Obama is clever and has a way with words: but his words contained little. He entranced audiences, first in his own party – which is why he beat Hillary Clinton, arrogant and boring then as now, for the nomination – and then in the wider electorate. John McCain – old, white, Republican and with the media’s hate figure, Sarah Palin, as his running mate – didn’t have a prayer.

The sobbing woman was white and middle-aged. The constituency which was most ecstatic about the arrival of the miracle-worker, the poor blacks, have been even harder done by. He cites an instructive article in the latest New Yorker, about evictions in Milwaukee, a city that is 40 per cent black. There, despite having been elected on a platform promising to end the misery of evictions, an industry now exists to service evictions – courts, lawyers, removal men, bailiffs – and operates full-time, dealing with masses who cannot pay their rent, or their mortgages.

Heffer says that while he doesn’t know Milwaukee, he is familiar with cities such as Baltimore, Newark and Trenton, which have square miles of squalor.

The racial tensions, which he as a black president was expected to heal have not lessened. Ferguson is still smouldering and trigger happy cops seem to turn up everywhere. There is no sense that law enforcement has become anymore user friendly that it ever was – and he clearly is getting nowhere on the issue of gun control. Add to all this, the feeling that his foreign policy is inept and worse. He has, Heffer says, largely removed America from international conversations.

After the disastrous interventions in the Islamic world after 2001 it is quite right it should think more deeply about such expeditions: but that does not mean the superpower’s global responsibility can be abdicated completely. The Kerry intervention in Syria last week was typically, and tragically, late. Mr Obama’s international legacy is the repulsive sight of Vladimir Putin, whom he underestimated, ruling the roost, the barbarians of Isil (for dealing with whom he had no strategy) and a Europe mired in introspection.

At this point, enter Donald Trump. For many, given this scenario, he is a fantasy knight in shining armour. Heffer notes, after ‘The Donald’s’ triumph in New Hampshire last week, how many of his voters complained of feeling that America was being kicked around in the world. A great nation that is being forced to confront its global impotence is one for whom the bombastic Mr Trump holds inevitable appeal; and an America with such deep-seated social and economic problems is one that will look to Bernie Sanders. After all, everything else has been tried, so why not what he calls “democratic socialism”?

The Obama era is almost over – but his legacy is a far cry from what was expected from him in those days when he too was the knight in shining armour. While America may have limply recovered from the financial collapse of 2008, it had relatively little to do with him. The sector dealt with the cycle like it has been doing off and on for two centuries and more. He does not seem to have done much to help America – and the rest of us who are dependent on its fortunes – to cope any more effectively with the next crisis which may be just around the corner. That this task may fall to one of the heirs-not-yet-apparent who are leading in their respective polls is indeed a worrying prospect. If his most abiding legacy is, as Heffer says, the creation of a space in which these two political aberrations have been able to thrive and capture the most powerful office on earth then we have reason to worry.

Heffer says that when he is gone no one will miss him, least of all the one-time allies who feel he has spurned them. He has, he says, made America much less relevant. That may be so, but looking around us at the world we live in today, we may well have reason to rue the irrelevance of a democracy which has done so much in the past to make the world a better place and, twice in the last century, lead it away from two horrific tyrannies.