If contemporary politics have taught us anything, it's that things can always get worse

President Trump is using crude racial rhetoric as a central plank of his re-election strategy

President Donald Trump's campaign supporters have chanted "send her back" about the Somali-born congtresswoman Ilhan Omar. AP

A friend of mine – a very clever economist – once told me that one of the biggest errors of politicians is to mistake a cycle for a trend. Markets rise and fall in the economic cycle. But when a market is doing well, political leaders often claim it is because their leadership and policies are wonderful, with the implication that as long as they are in power, as Tony Blair's supporters put it, "things can only get better".

That’s simply not true. They can get much worse, too. Donald Trump may find this out when the US economy – which is generally doing very well – eventually takes a dip, perhaps in time for his re-election bid next year. Of course, when things go badly in the next part of the cycle, those same politicians generally cast the blame elsewhere. “Global economic factors” offer a good excuse. Or “the slowdown in China.” Or “political uncertainty in the Eurozone.” Or “fluctuations in energy prices.”

My friend the economist was making the point that markets are like the sea, and politicians can navigate them, but they do not make the weather. I’ve also been pondering this difference between a cycle and a trend in other matters. Race relations in the United States, for example.

When I first lived in Washington DC in 1989, roughly 75 per cent of the population were African-American. But the neighbourhood where I lived was almost completely white. African-American workers staffed the local supermarket, but they came from another part of town. The one person of colour who actually lived near me was a diplomat from the Caribbean. At first, I thought this was simply an economic issue, that expensive housing where I lived priced African-Americans out of the market. Then I discovered that many middle-class African-Americans chose to live in middle-class African-American suburbs. Then I decided to join a gym. The first two I tried were almost entirely white, presumably reflecting the population of the areas they served, so I joined the downtown YMCA gym, which reflected all races in the city.

What is astonishing is not that Mr Trump speaks and acts crassly, derides women and uses age-old racist tropes. It is that prominent members of the Republican Party refuse to criticise him for it

During the Clinton years US race relations appeared to change. Some African Americans – who tended to be big Clinton supporters – used to joke that he was the "first black president." I thought there was a trend to heal the wounds of slavery and racism, and that trend developed even more when Barack Obama really did become the first African-American president. Awareness and consciousness of these issues started to mean that people criticised the Oscars for a lack of racial balance. I met Ava DuVernay, the director of Selma and 13, and we talked about the lack of women and African American film-makers in Hollywood. The rallying cry #OscarsSoWhite seemed to help white people think about being more inclusive. Again, I thought there was a trend – that talented women and African-Americans would be recognised for their gifts and hard work, and that this trend of better race relations would take time to bear fruit, but never stop.

I was wrong. It has stopped. My optimism had initially been captured by Rodney King, a black man whose beating by Los Angeles police sparked riots in 1992. Even after his brutal ordeal, he implored people that it was better to "just get along." Every American friend of mine agreed with that sentiment. Today, President Donald Trump seems not to at all. He has indulged in public race baiting of a type I thought had been consigned to history, along with Jim Crow laws and segregated water fountains. Trump's Tweets about sending four congresswomen back home, when all four are US citizens and three of the four were born in the United States, are crudely racist at best. They also prompted a crowd of Trump supporters at a rally to chant "send her back" about the congresswoman Ilhan Omar, who was born in Somalia. Mr Trump has suggested that he felt bad about this, but if that were true he could have told the crowd to stop.

What is astonishing is not that Mr Trump speaks and acts crassly, derides women and uses age-old racist tropes. It is that many prominent members of the Republican Party refuse to criticise him for it. And that 40 per cent of voters either do not notice or do not care. And here is another cycle that has not become a trend. During the Clinton presidency a key adviser explained to me how Clinton won elections. The adviser held his hands out, wide apart and said that if Republicans and Democrats were this far apart, then all the votes in the middle were up for grabs. He moved his Left hand far to the Right, saying that the closer Clinton moves towards his opponent, the more votes in the middle Clinton receives. Donald Trump has destroyed the middle ground, but in an entirely different way. His strategy for 2020 is to maximise his base support, by stirring up as much racial tension as possible. Will voters in the centre turn away from him? That very much depends if there are any voters left there.