To critique Barack Obama’s presidency is to be guilty of these cardinal sins: blasphemy, ingratitude and a lack of realism. What was once the nation of Jim Crow produced the first African-American president, the most liberal commander-in-chief since Richard Nixon (as Obama himself once put it). Funny, charming, with a coolness that eludes practically every other politician, he is the ultimate ambassador for US power. Could the United States possibly elect someone more progressive?

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And yet it is difficult not to conclude that, as Obama delivers his final State of the Union address, the US remains a chronically unjust and devastatingly unequal society, its proud democracy beholden to powerful and wealthy interests. It is this potential tinderbox that makes the implausibly clown-like, quasi-fascist Donald Trump the Republican frontrunner; and, more hopefully, a 74-year-old self-described socialist from Vermont – Bernie Sanders –a serious challenger to the Clinton machine.

That’s not to diminish Obama’s achievements. The lack of universal healthcare has long made the US a baffling aberration among developed nations; Obamacare’s significantly increased coverage should not be sniffed at. Obama’s U-turn on his public stance on equal marriage – yes, made possible by the struggle and sacrifice of US LGBT activists – is another triumph. His recent activism on the great US guns scandal and the existential threat of climate change is to be applauded, too.

But consider the plight of the majority of Americans. We know that, six years into his presidency, poverty was still higher than before the financial system near-imploded. While child poverty has been alleviated for many Americans in the past five years, for African-Americans it has remained stubbornly constant.

The gains of economic recovery have certainly been beneficial to those of great wealth – including the culprits behind the crash – but have meant little to the average American. Of course, that has everything to do with the structure of the US economy since Ronald Reagan swept to power. Consider this: according to the Economic Policy Institute – a thinktank close to the embattled US labour movement – between 1979 and 2007, the top 1% seized 53.9% of the entire increase in US income. It is often suggested that male median income has been stagnant in the US since the 1970s, hidden only by a flood of women into the workforce: how that’s worked out depends on all sorts of qualifications, such as which price index you choose. Yet even by the most optimistic calculations, if university-educated American men have enjoyed a boost in salaries, those with only high school qualifications endured sliding incomes between 1979 and 2013.

But if Reaganism engineered this model, Obamaism failed to replace it. According to Emmanuel Saez, a US economics professor, between Obama’s inauguration in 2009 and 2013, pre-tax income among the top 1% has jumped from $871,100 to $968,000; for everybody else, it practically stood still.

Yes, the top 1% suffered a bigger hit in the crash (but how they bounced back), employers’ healthcare contributions have to be factored in, and Obama’s administration introduced a more progressive tax system than the one Bush bequeathed. Yet here is an economy structurally geared to favour the very wealthiest. A woman in a full-time job takes home the same paypacket as she did in 2007; a man, slightly less. In 2014, hourly wages after inflation were falling or flatlining for most American workers. US workers might be more productive, but they will struggle to see the gains in their bank balances.

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That’s before we even deal with foreign policy. We all know of Bush’s Iraq folly, opposed by Obama himself; but, as Isis marches across the coast of chaos-ravaged Libya, we spend too little time addressing the president’s own foreign calamity. Drones that former US service personnel have described as recruiting sergeants for Isis; the failure to redeem his promise to shut Guantánamo; the failure to secure a just peace in Palestine.

Across the western world, popular discontent is either being funnelled into the ranks of the xenophobic populist right, or new progressive movements of the left. For all too many struggling middle-income and poor Americans, it is Trump who has become the answer, directing their anger at anyone but the powerful. But whether or not Bernie Sanders secures the nomination, his movement offers some hope to cure the ills of modern America.

Without the support of Big Money, Sanders’s grassroots campaign raised $73m last year. With primary elections looming, Hillary Clinton is now in a dead heat with Sanders in Iowa; in New Hampshire, he is ahead. His movement could transform the Democratic party.

None of this is to scapegoat Obama. Even the most well-intentioned president will struggle against a system described last year by Princeton researchers as an “oligarchy”, where the median net worth of a senator in 2013 was $2.8m. But fewer Americans are self-identifying as conservative; younger Americans have far more progressive views than their elders. Black Lives Matter and Occupy have forced long-ignored issues on to the agenda.

Obama’s presidency has failed to build the just America its citizens deserve. But the US has a proud history of bottom-up movements that have overcome injustice. Their time may have come again.

• This article was amended on 14 January 2016. An earlier version referred to “the Democrat party”, where it should have said “the Democratic party”.