Blink and you miss it. It really isn’t much of a public holiday, midway through the most miserable month of the year a break you don’t need after all the days off during an all-too-recent festive season. The day feels utterly normal until you venture out to the bank or the local public swimming pool, only to find them shut. But here we are. It’s the third Monday of January again, cold and grey. In the US that means Martin Luther King Day.

It wasn’t a marker the country seemed to want very much either. The first demands for a holiday to honour the guiding force of America’s civil rights movement came from black leaders, just a few days after King’s assassination in April 1968. But it took 15 years to move a bill through Congress and its shoals of concealed racism, and be signed into law by an unconvinced President Ronald Reagan. Even now some Southern states use the date to celebrate the birth of the slavist Confederacy’s great military hero Robert E Lee (born 19 January), alongside King (born 15 January).

In 2017 though, Martin Luther King Day is a perfect bookend for a week that could prove a watershed of modern US history. It’ll start with a reminder of one of the greatest Americans and his still unfinished work, amid the very final days of the country’s first black president, a notion that must have been unimaginable to King – or at least so soon, barely 40 years after his death.

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And the end of the week? The country that has just bowed its head, albeit briefly, to the supreme champion of the fight against racism will inaugurate Donald Trump, who played footsy with white supremacists and whose bigoted rants against Mexicans, Muslims and the like helped him win the White House. King was about helping his people, long downtrodden, to attain their basic human right of living in a society equal for all. Trump is about just one thing: Donald Trump.

You can be sure he’ll find a way of turning Inauguration Day, the most sacred of America’s constitutional pageants, into just another moment of self-glorification, even though he’s taking office as the most unpopular president ever (his approval rating is just 44 per cent, according to a Gallup poll last week – and that before the latest uproar involving Russia.) For a while some hoped a post-election “new” Trump might emerge, sobered by the huge responsibilities of his new office.

Not a bit of it. As that press conference last week showed, Trump the president-elect is identical to Trump the candidate: bombastic, bullying and insulting, irredeemably ignorant, on any issue tweeting out the first thing that came into his head; a perennial showman with an ego of a size matched only by its fragility. But why should a 70-year-old man change his ways, after a hugely successful business career? If it ain’t broke, don’t fix it.

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Needless to say the paths of King and Trump haven’t crossed very often. But they did on the campaign trail last year, on King’s holiday. Trump had been invited to hold a rally that day at the Christian college of Liberty University in Virginia, founded by the late Jerry Falwell Sr, televangelist and leader of the Reagan-era Moral Majority movement.

The date and the event, on the eve of the primary season, had been specifically designed to improve his credentials with the Christian right, an important Republican constituency that was, for understandable reasons, still leery of Trump and was being wooed by bona fide social conservatives like Ted Cruz and Ben Carson.

Predictably, candidate Trump sank to the occasion, making just a couple of references to King, and self-aggrandising ones at that. As usual his obsession was himself — this time measured by the size of the crowd, estimated at around 10,000.

“It’s an honour to be here, and especially on Martin Luther King Day,” Trump began.

“We broke the record – we had the record for about three or four years the last time, and the first thing I said to Jerry and Becki [Falwell Jr] when I got here, ‘Did we break the record?’ They said, ‘Yes, you did, by quite a bit’. So we’ll dedicate that to Martin Luther King, a great man. And that’s a little bit of an achievement, I will tell you.”

If Trump has managed to refrain from such bragging by this time next week, it’ll be a miracle, and if King had been around to hear Trump’s words at Liberty University, he would have raised a wan smile. The rest of us can muse on the moral and qualitative decline of American leadership, neatly compressed into seven days.

King might have spoken the language of historical impatience. “We come here tonight to be saved from that patience that makes us patient with anything less than freedom and justice,” he said at a rally when Rosa Parks was arrested for not giving up her seat on a bus in segregated Montgomery, Alabama, in December 1955.

In reality though, he had an almost inhuman patience, above all in his insistence that the civil rights movement remain non-violent, whatever the provocation. Trump by contrast is all impatience and bluster. Oddly, he’s more flexible than King – but that’s only because a tiny attention span allows him to forget his previous stance on an issue. King, unbending in the pursuit of his aims, would never forget.

And as for the difference in styles — King’s dignity against Trump’s coarseness — don’t even mention it: “I have a dream” against ”Hillary – guilty as hell”? All they share is the distinction of being investigated by the FBI for possible Russian links: Trump in connection with the 2016 campaign, King for alleged links with the Communist party in the 1950s and 1960s.