You've got to feel sorry for the Democratic ­Senate leader, Harry Reid. In 1995, when it seemed Colin Powell might run for president, Powell explained his ­appeal to white voters thus: "I speak reasonably well, like a white person", and, visually, "I ain't that black".

More than a decade later, Reid said almost the same thing about Barack Obama, arguing that the presidential candidate owed his success in part to his "light-skinned" appearance and the fact that he spoke "with no Negro dialect, unless he wanted to have one".

There is a crucial difference here (leaving aside that Reid has not updated his terminology since the 50s). Powell was talking about himself and is black, while Reid was referring to someone else and is not. But if the ensuing ­brouhaha was embarrassing for Reid – on those rare occasions when Fox News finds a sliver on the high ground, it tends to take out a long mortgage and build on it – it was emblematic of a far bigger issue for Obama.

Because on top of an economy in ­collapse, two wars unravelling and plummeting approval ratings, he has what can best be described as a ­"discursive" problem.

A full year after he took office, people have not found a sensible way to talk about him. One minute Jesse Jackson, in an unscripted moment, says he wants to "cut his nuts off"; the next he is crying in Chicago's Grant Park as Obama delivers his victory speech. The same people on the right who insist he is a Muslim fulminated over his pastor, ­Jeremiah Wright. When you point out that Muslims don't have pastors, they just shrug. Europeans who wish he led their country also wish their countries would pull their troops out of Afghanistan – the very war he is escalating.

When it comes to Obama, it really doesn't have to make sense – it just has to connect. Those who misunderstood how Obama came to office are now struggling to understand what has ­happened in the year since he has been in it for three main reasons.

First, Obama was never a radical. He won on a decidedly middle-of-the-road Democratic platform. Beyond the Iraq war, which he opposed and she ­supported, there was little to chose between him and Hillary Clinton in terms of their programmes. They had voted the same way in the Senate 90% of the time.

True, he represents a dramatic progressive shift in direction from the previous eight years. But in almost any other western country his policies on the Middle East, gay marriage, trade and capital punishment would cast him out of polite leftwing company. Yes, there are grounds for disappointment. Bush's torture infrastructure has been left largely intact, the Iraq withdrawal has been extended by two years and the healthcare reform debate might have panned out differently had he led more decisively. But there is a world between that and accusations of betrayal and treachery. In Afghanistan in particular, the problem was that he kept his campaign pledge whereas many of us wish that he had broken it.

"Why as an intellectual did you believe in a God anyway," asked the ­Palestinian intellectual Edward Said after rereading The God That Failed, a book in which six prominent ex-communists relate their disillusionment with communism. "And besides, who gave you the right to imagine that your early disbelief and later disenchantment were so important?" Those who think they have been let down by a leftwing champion must answer for their own selective hearing.

What really distinguished Obama's campaign from Clinton's was its ­grassroots energy. Which brings us to the ­second point. While it was a grassroots campaign, it was never a movement. That didn't mean there wasn't the possibility that it might have become one. But its sole function was to get him elected. When you pointed this out to his supporters during the election, many would become indignant. But one year on, the question is: "Where are they now?" In a handful of areas, the energy and determination of those days is still evident. But for most of this year the right has been making all the running outside of the electoral politics and forcing the administration on to the back foot. It is reasonable to argue that Obama should tack to the left. But given the range of forces he has to deal with, from Fox News to corporate lobbyists, it is not reasonable to argue that he would make that leftward journey without some pressure from outside or to expect him to organise the left opposition himself.

Finally, for all his financial and organisational advantage, the fact that he ran a far better campaign, had a far more impressive running mate, was a far more charismatic candidate, and was campaigning against a party that had overseen a huge economic crisis and two unpopular wars, Obama did not win by much. In terms of the popular vote he won 53% of the vote against John McCain's 47%. True, there were 192 electoral college votes between them. But 73 of those – Florida, Ohio, North Carolina and Indiana – were won with just 51% of the vote or less.

When it comes to health reform and the economic stimulus bill, Obama may reasonably be accused of timidity in ­promoting a more progressive agenda, but only in the context of what is legislatively possible. He needs 60 votes in the Senate to get a bill passed. No 60, no bill.

All of this comes by way of critique rather than criticism, and explanation as opposed to ­excuse. Obama does not need the benefit of our doubt. He is the president of the most powerful country on the planet. He has enough benefits already. But the absence of rational discussion will lead, ­ineluctably, to the absence of rational conclusions. Tomorrow being Martin Luther King day, those who want to compare him to the civil rights leader must first acknowledge that King never had to stand for election. If he did, he would certainly have lost. We are only still talking about Obama because he won. And his victory was secured with narrow margins on a mainstream agenda. One need not accept these limitations in ­order to acknowledge their existence.

What the response to his election indicated was a sizeable constituency, both at home and abroad, for a shift towards greater peace and equality than the politics that dominated the last decade. But, given the entrenched interests in the American polity, no election by itself can deliver that. The distance between the aspirations invested in him during his campaign and his record after one year is the distinction between the electoral and the political in this current period. Popular demands thwarted by institutional stasis and ideological sclerosis.

These are early days. But the risk at this moment is twofold. First, that Obama ends this year with no progressive legislative victories. Second, and arguably worse, that he embraces legislation that sounds progressive but does not substantially improve people's lives. People don't want healthcare reform; they want affordable healthcare. They don't want a stimulus bill; they want jobs. The time for lofty rhetoric has long gone. The time for measured analysis has been too long coming.

• This article was amended on 18 January 2010. It originally stated that there were 92 electoral college votes between Obama and McCain. There were 192. This has been corrected.