I was just recalling how, about a year ago, my country was swept up in a spasm of self-congratulation. Not only had Barack Obama broken a seemingly insuperable historical barrier in winning the presidency, the media told us, but "we" had as well. We had overcome centuries of gruesome history and proved to the world that America could live up to its promise.

The US press in those days duly reported but tended to downplay events that told the opposite story. The footnote, for instance, that the white supremacist website stormfront.org temporarily went dead on 5 November, the day after the election, because it was so inundated with requests for membership. And the tale about the Maine convenience store that started an "Osama Obama Shotgun Pool" inviting customers to bet on the date Obama would be shot, and saying: "Let's hope we have a winner".

These were treated as isolated events, and maybe they were. The important thing was the people had spoken, and they'd given proof that America wasn't that kind of country any more.

A year later, we've seen an epidemic of hatred against the president that I think is safe to call unprecedented. Bill Clinton and George W Bush were hated – but not quite like this. When we have a pastor, a real-live Baptist minister in Arizona, devoting a sermon to explaining why the president should "melt like a snail" (and he was explicit – he meant Obama should be killed), we've reached a new point. Obama, it was reported over the summer, receives 30 death threats a day, three or four times the number issued against Bush. And I think it can't be just a coincidence that you will almost never see him give a speech out of doors, the middle of a heavily guarded military base (Fort Hood) providing a recent and rare exception.

We're not supposed to talk about race as a motivator for these kinds of things in this country. There are some decent reasons why. First, it's said, the anger felt towards Obama – among the "tea party" contingent, for instance – is in the main ideological. Let me be clear: I agree with this. It is in the main ideological. What a lot of the rest of us see as salvaging hundreds of thousands of jobs and averting a far deeper crisis by taking steps to bail out General Motors, Chrysler, Citigroup and Bank of America, they see as socialism. Fine. It's a free country, as we like to say.

Second, race is hard to talk about because it's unquantifiable. If an incident occurs that looks as if it might be a hate crime but contains shadings of ambiguity, we can't say, "Well, that act had roots that were 61% economic and 39% racial". Likewise with Obama hatred. And if something can't be measured, it's hard even to argue about, let alone agree on.

And third, I do think it's fair to say that, at this point in US history, most individuals aren't racist, at least in any blatant way. Most white people, especially from middle age down, may have a black friend or two, or at least co-workers with whom they get along fine. When conservatives complain that they feel they can't make criticisms of Obama without being called racist, they have a point, and on an individual level I have some sympathy with them.

But here's the thing that most media discussions of race miss. It has to do with the difference between the individual and the crowd.

The tea partiers are about 98% white. I went to the 12 September tea party march at the Capitol building. I saw many thousands of people. I spotted about a half dozen Asians, three or four Latinos, and one black person. All the rest were white. Look at the videos from the town halls over the summer. Virtually all of the angry people are white. Look, indeed, at the Republican party. It's almost entirely white. Yes, Michael Steele, a black man, is its chairman. But he was obviously a strategic and even cynical choice (made after Obama was elected) and was not culled from the ranks of numerous available black Republicans, because in truth there are hardly any.

Add to this the fact that it is a central article of faith for American conservatism that the whole business of diversity is nothing but a racket, forced on them by liberal elites. I can't think of one measure meant to ameliorate America's hideous history of racial discrimination that conservatives have supported. Literally not one, in the 50 years we've been trying them.

This is the Obama-hating crowd. It's deeply conservative, and it's about 98% white. And the thing about crowds is that they develop a personality of their own that is not merely the sum of individual parts. A crowd is an organism that grows in its own way and tends to be led and excited by its extremes. It can mutate into being racist without many or even most of the individuals in it being so.

It can be a danger, as we're often reminded, to overstate these things without that magical "proof" we're always looking for. But the greater danger rests in understating them. Americans resist overstatement because we want to reassure ourselves we're a good country at heart. But history has more often proved on this topic that we're not. We'd do well not to forget that.