In case you hadn’t noticed, he’s back. Vainer, more bombastic and more preposterous than ever, Donald Trump is running for president again. And the Republican Party to which (for now at least) he belongs, is scared out of its wits.

We have, of course, been here before. In 2000, Trump was a candidate of the Reform Party founded by Ross Perot. In three other elections he’s floated the idea of competing in the Republican primaries – most recently in 2012, when the mere possibility of a Trump bid for the White House saw him briefly top the polls, admittedly against a weak Republican field. In the end, he decided not to run. This time, however, he is running, against one of the biggest and most qualified fields in memory. And guess what? He’s leading the pack again.

An Economist/YouGov poll on Friday had him at 15 per cent among registered Republican voters, four points clear of Jeb Bush, and well ahead of the other two favourites for the nomination, Marco Rubio and Scott Walker, not to mention the likes of Chris Christie, Rand Paul, Rick Perry et al.

Now, this is the silly season for US presidential politics, almost seven months before the Iowa caucuses kick off the primary season. Cast your mind back to the same moment of the last election cycle, in high summer 2011. Leading the Republican pack was the pizza magnate Herman Cain (he of “I don’t know who’s president of Ubeki-beki-beki-beki-stan-stan”), followed by Michele Bachmann, fire-breathing queen of the Tea Party. Both candidacies ultimately sank without trace.

Donald Trump's most controversial quotes Show all 14 1 /14 Donald Trump's most controversial quotes Donald Trump's most controversial quotes On Isis: "Some of the candidates, they went in and didn’t know the air conditioner didn’t work and sweated like dogs, and they didn’t know the room was too big because they didn’t have anybody there. How are they going to beat ISIS?" Getty Donald Trump's most controversial quotes On immigration: "I will build a great wall — and nobody builds walls better than me, believe me —and I’ll build them very inexpensively. I will build a great, great wall on our southern border, and I will make Mexico pay for that wall. Mark my words." Reuters Donald Trump's most controversial quotes On Free Trade: "Free trade is terrible. Free trade can be wonderful if you have smart people. But we have stupid people." PAUL J. RICHARDS | AFP | Getty Images Donald Trump's most controversial quotes On Mexicans: "When Mexico sends its people, they’re not sending their best. They’re sending people that have lots of problems. They’re bringing drugs. They’re bringing crime. They’re rapists." Getty Donald Trump's most controversial quotes On China: "I just sold an apartment for $15 million to somebody from China. Am I supposed to dislike them?... I love China. The biggest bank in the world is from China. You know where their United States headquarters is located? In this building, in Trump Tower." Getty Images Donald Trump's most controversial quotes On work: "If you're interested in 'balancing' work and pleasure, stop trying to balance them. Instead make your work more pleasurable." AP Donald Trump's most controversial quotes On success: "What separates the winners from the losers is how a person reacts to each new twist of fate." Donald Trump's most controversial quotes On life: "Everything in life is luck." AFP Donald Trump's most controversial quotes On ambition: "You have to think anyway, so why not think big?" Getty Images Donald Trump's most controversial quotes On his opponents: "Bush is totally in favour of Common Core. I don't see how he can possibly get the nomination. He's weak on immigration. He's in favour of Common Core. How the hell can you vote for this guy? You just can't do it." Reuters Donald Trump's most controversial quotes On Obamacare: "You have to be hit by a tractor, literally, a tractor, to use it, because the deductibles are so high. It's virtually useless. And remember the $5 billion web site?... I have so many web sites, I have them all over the place. I hire people, they do a web site. It costs me $3." Getty Images Donald Trump's most controversial quotes On Barack Obama: "Obama is going to be out playing golf. He might be on one of my courses. I would invite him. I have the best courses in the world. I have one right next to the White House." PA Donald Trump's most controversial quotes On himself: "Love him or hate him, Trump is a man who is certain about what he wants and sets out to get it, no holds barred. Women find his power almost as much of a turn-on as his money." Getty Images Donald Trump's most controversial quotes On America: "The American Dream is dead. But if I get elected president I will bring it back bigger and better and stronger than ever before and we will make America great again." GETTY

Fast forward to 2016, and Trump is their natural successor, an endless source of quotes and headlines, ideal political entertainment as the dog days beckon. Except, that is, if you’re part of the Republican establishment. There, the conventional wisdom – or perhaps wishful thinking – is that Trump will fizzle like Cain and Bachmann, as soon as chilly autumn signals a return to political common sense. But Trump says he’ll be around, in one guise or another, for a good deal longer. If so, then the GOP brand that party elders are trying so hard to rebuild risks a real beating.

Those fears began the very day Trump formally announced his candidacy at his eponymous Tower in New York a month ago. His focus was on immigration, the most sensitive single issue for Republicans as they seek to improve on Mitt Romney’s dismal showing in 2012, when he won just 27 per cent of the Hispanic vote, a failure that guaranteed his defeat.

“The Donald”, though, was having none of it. “When Mexico sends its people, they’re not sending their best…. They’re sending people that have lots of problems, and they’re bringing those problems with them. They’re bringing drugs. They’re bringing crime. They’re rapists.... And some, I assume,” he added with withering condescension, “are good people.”

Republican grandees were aghast, the immigrant community was in uproar, and Democrats could not contain their glee – especially because Trump, far from back-pedalling, doubled down on his claims. Every illegal immigrant was a “potential rapist” he later declared on CNN, demanding that Mexico build a wall to keep them out. Naturally, he professed love for Mexico. “This isn’t just about Mexicans. I’m talking about people that are from all over that are killers and rapists and they’re coming into this country.”

Predictably, many doing business with the great self-promoter, among them NBC, Macy’s and the Professional Golfers’ Association, have fled for the exits. José Andrés, the Spanish super-star chef, has cancelled plans for a restaurant in the de luxe hotel that Trump is building here in Washington. But every rebuff, it seems, only makes Trump more popular – even the revelation that construction workers at the hotel are mostly immigrants, some of them presumably illegals.

Real estate mogul and TV personality Donald Trump announced his campaign for the 2016 Republican presidential nomination last month (Getty) (Getty Images)

And the megalomania only grows. The other day, Reince Priebus, the Republican party chairman, called Trump, asking him, we were told, to “cool it”. The property mogul quickly put Priebus in his place. It was a “congratulatory call,” he told The Washington Post: “He’s going to lecture me? Give me a break.” Giant egos do not slip quietly into the good night.

But some interested parties have been notably quiet. I refer to Trump’s competitors for the nomination. Yes, a few, notably Bush and Rubio, have chastised him, but belatedly and relatively gently. The silence speaks volumes about the Republicans’ dilemma. Detest Trump if you will, but on immigration he’s telling the party’s core electorate – older white voters, this time more important than ever given the party’s problems with blacks, Hispanics and other minorities – just what it wants to hear.

Not only on immigration. If you’re fed up with Obama’s caution in the Middle East, how sweet “the Donald” must sound. A President Trump would “bomb the hell” out of Iraq’s oilfields to strike at Islamic State. As for US troops on the ground, forget it: “You won’t need ’em by the time I’m done.”

This confronts Priebus and the establishment with a double nightmare. The first is Trump’s participation in the first candidates’ debate on 6 August. Given that he easily qualifies among the top 10 candidates measured by the polls, he can hardly be denied a spot. He might make an idiot of himself. Equally likely, though, he’ll upstage everyone with his soundbites, handing yet more election ammunition to the Democrats.