Yasmin Alibhai-Brown: Is this President still worthy of the hope we pinned on him?

President Obama arrives for a state visit to Britain this week, and there is much excitement at my gym where I am wearing my Obama T-shirt, his face on my chest as I wheeze and walk and sweat on the treadmill. Several other exercisers say the man is "cool", "some dude", "one special guy". The most enthusiastic are black men. Tony, for example – a sweet man and a big bouncer who would pay a thousand pounds just to see the face of the President when he comes to London: "He shows we are not born to be slaves, but to be top man. He gave us back pride, man, real pride." Tony's emotions stir mine.

How can one not be moved by the story? Obama is a natural outsider, the son of a Kenyan man and a white American woman, stepson of a Muslim Indonesian. Tea Party and Republican crazies are panicked by his complex background; he's not black enough for some African Americans and is a suburban nightmare – the product of a wayward hippie who betrayed her race not once but twice. Somehow, he disabled these entrenched racial prejudices, vaulted over ramparts, penetrated the defences around the houses of power and did so with acumen and unrivalled grace. Millions of us fell in love with him then. I still am for President Obama, but am less inclined to believe in him or the future as much as I did the day he walked into the White House. The image on the T-shirt is fading.

This isn't the predictable confession of a foolish idealist – the usual plunge of excessive optimism as the daily, dirty business of governance takes over after elections. Compromises have to be made by those who attain political power. Obama, though, is going way beyond that. I said on a recent edition of Question Time that he seems to be turning into an ugly American, too often speaking and acting to mollify Sarah Palin and other right-wing detractors. There were early signs that the President didn't have the will to stick with unpopular, principled decisions. Guantanamo Bay is still open, visible proof that the majestic US constitution is disregarded when Americans are tested as they were when they were attacked on 9/11. The custodian of that foundational declaration continues to violate its tenets.

He ordered the execution of Bin Laden and now warns that other similar raids may be carried out. Does he think that others thereby have the right to enter his country and execute people they blame for world unrest? What kind of example is the US setting? He also claims that even before Bin Laden's death, "al-Qa'ida was losing its struggle for relevance, as the overwhelming majority of people saw that the slaughter of innocents did not answer their cries for a better life". He has also said that by the time they got Bin Laden, al-Qa'ida had reached a "dead end". So why did he order the killing? Such deplorable and unworthy cowboy antics from one so wise and a lawyer.

I get much abuse for saying so, but Bin Laden should have been brought to trial. The US should not be allowed to opt out of the International Court in the Hague or go around shooting to kill at will. Obama has yet to acknowledge that countless non-American innocents have been killed by the Taliban, al-Qa'ida, US and other western weapons, including in Iraq and Kenya, homeland of his father. The born-and-bred internationalist – multilateralist – seems to believe that US lives are intrinsically more valuable than the lives of those in the developing world. His Libyan intervention is going badly wrong and showing up disastrous inconsistencies. Being non-white doesn't give Mr President immunity from fair criticism. Those of us who supported him must not shirk from that responsibility.

Americans who voted for this President now appear divided on his policy achievements and fudges. Early enthusiasm is chilling. The Princeton professor Cornel West, an African-American himself, recently blasted Obama for being a "black mascot" of Wall Street; the singer Harry Belafonte has been just as scathing. The President apparently scolded these men and asked them to cut him some slack. Inequality is rising, and the poorest are paying the highest price for the global economic crisis. No one expected George W Bush to care about the lost souls of America. Today there are near Great Depression levels of unemployment in black neighbourhoods. Obama was meant to give them back fair chances and dignity. He promised.

Those who side with West and Belafonte believe now it is no longer enough for Obama to be judged for what he is, but what he does. Dr Wilmer J Leon III, a black talk-show host and political scientist, believes that "having an African-American in power is not in-and-of-itself a victory", and rejects the refrain that it would be much worse under another leader.

Al Sharpton and others, including white commentators, have stood up for the President, who is, after all, the head of the whole nation, not only people of colour. His critics ignore how much he has got done. Some health reforms went through in spite of huge opposition, as did tax breaks for the poor, consumer protection and key education measures.

T he President's latest speech on the Middle East, though still tilted too much towards Israeli interests, provides real, substantive possibilities for a two-state solution based on 1967 borders. He seems genuinely affected and humbled by the Arab Spring, and understands that the US cannot go on back-slapping Arab dictators. But the good stuff cannot offset the failures in the political ledger.

Obama's message was "the audacity of hope". When that popular optimism is dashed, wrote Martin Luther King, "hate is often turned most bitterly towards those who originally built up that hope". Too many who believed in Obama are now bitter. He could still be, in my view, one of the greatest leaders of the free world – if he heeds the voiceless in America and lives up to his own moral credo abroad.

In Cairo in 2009, Obama said human beings needed "to have confidence in the rule of law and the equal administration of justice". That means no imprisonments without trial, no assassinations, no indiscriminate drone attacks, no special rights for the superpower, no excuses for injustice and inequality. Can he deliver that? Yes he CAN! I hope.

y.alibhaibrown@independent.co.uk