Donald Trump wins Indiana and sees the finish line in the Republican Party's amazing race

Take the back entrance into Trump Tower and you’ll spy the orange slogan painted down both sides of the short white corridor. “There is no finish line,” it says. The message is courtesy of an athletic footwear store next door, but on this night it might have been meant only for the man with big hair.

As he strode out into the main foyer of his signature skyscraper that boasts his name to bask, once more, in the glow of victory, Mr Trump nonetheless had the look of a marathon runner who had, in fact, not only found the finishing line but also crossed it.

The billionaire-turned-novice-politician had indeed done something rather bigger than just winning the primary of the day, which happened to be far way in Indiana. He had done it in such a decisive, overwhelming way that he had also managed, as if almost by accident, to dispatch his chief remaining rival, Senator Ted Cruz of Texas, from the field in the process.

That announcement had reached Trumpland via TV sets along the foyer’s marbled walls, volume twisted to the max. Mr Cruz, speaking in Indiana, uttered the words “suspend my campaign” and the black-suited courtiers of Trump – supporters and campaign staff - arrayed three deep behind the podium at which he was about to speak allowed themselves first to cheer before reverting to polite but emphatic applause.

“It’s been some unbelievable day, and evening and year...I have never been in anything like this. But it’s a beautiful thing to be in and a beautiful thing to behold. And we are going to make America great again!” mused Mr Trump moments later, his wife, Melania, and his three grown-up children, Ivanka, Eric and Donald Jr, at his side. Under his watch America will become “one great, loving country,” he offered.

The removal of Mr Cruz from the equation means Mr Trump will assuredly glide now to the 1,275 delegate tally he needs to secure his party’s nomination ahead of the national convention in Cleveland in July. Only Governor John Kasich of Ohio stubbornly remains in his way. But he is barely a speed bump. All talk of a contested convention with devastating fights on the floor will now go away.

Hence the winner’s look. By Tuesday night, Mr Trump had seen off no fewer than 15 rivals for the Republican crown. In perhaps one of his calmest, most controlled and even most gracious of appearances, he paid fulsome tribute to Mr Cruz. “I don’t know if he likes me or doesn’t like me, but he is one Hell of a competitor. He has an amazing future and I want to congratulate him.”

But the real finish remains far, far away, of course. It will be one thing for Mr Trump to seize the Republican Party nomination in 2016 – one miraculous, previously unthinkable, thrilling (or thrillingly cataclysmic) thing – but another for him to repeat the act once the general election proper begins and actually win the White House in November, presumably against Democrat opponent Hillary Clinton.

Instantly, Mr Trump will have to start working toward making that plausible. That will above all mean turning his baleful canons on “crooked Hillary”, as he now calls Ms Clinton. In many respects, the battle between the two heavy-weight contenders starts now. It will be a blockbuster.

He started at her in the Tower in fact, announcing that soon-to-vote West Virginia is on his travel schedule for the next few days, a state, he said, where Ms Clinton was treating out-of-work coal miners as if they were numbers. “We are going to get those miners back to work,” he promised.

“We are going after Hillary Clinton, she will not be a great president, she will not be a good president, she will be a poor president. She does not understand trade. Her husband signed perhaps in the history of the world the single worst trade deal ever done. It’s called NAFTA (which set free trade between the US, Canada and Mexico).”

And watch how he and his newly expanded team of advisers try to sweep away some of the crockery he has broken in his 11-month journey here and attempt to persuade a reluctant, shell-shocked Republican Party to rally behind him. The effort will be led by Paul Manafort, newly hired to “professionalise” the Trump campaign and who was among those lurking closest to the boss as he spoke at the microphone.

“We have to bring unity to the Republican Party, we have to bring unity,” Mr Trump said, reporting that people who used to call him the “worst things” are now telephoning him asking to “get on the Trump train”. They are able to do it, he quipped, because “they are politicians”.

Maybe they phoning. The first sign that he is succeeding will be one or more high-profile endorsements from recognizable and big Republican names even as soon as this week. Although even that necessity was downplayed by Corey Lewandowski, the campaign manager, on Tuesday night. “Of course, we will welcome endorsements of Trump from anyone who wants to endorse Mr Trump,” he told The Independent. “We have been endorsed by 10 million voters and that’s what matters.”

Mr Trump has already asserted he doesn’t need the Party establishment – the party donors, officials and assorted donors and grandees – and he can win the big white mansion on Pennsylvania Avenue with the support of ordinary voters.

That is theoretically possible, but with roughly two thirds of Americans still telling pollsters they don’t approve of Mr Trump – and surely many despising him - getting enough voters behind him remains a very high mountain indeed, at the top of which there may or may not be a finish line waiting for him.