At about eight-thirty last night, after the news came in that Donald Trump had trounced Marco Rubio in Florida, and that Hillary Clinton had won big victories over Bernie Sanders in Florida and North Carolina, Tony Fratto, who was a White House spokesman for George W. Bush’s Administration, tweeted, “What essentially happened today is @HillaryClinton was elected president. We have 8 months of hyperventilating before its official.”

Since overstatement is the norm on Twitter, this divination perhaps didn’t merit much attention, taken on its own. But it reflected a growing belief among Republicans in Washington that Donald Trump and Hillary Clinton are unstoppable and that, come November, this will spell disaster for the Grand Old Party. By the end of the night on this Ides of March, the third successive primary Tuesday, the gloom in the Republican establishment had deepened further, as both Clinton and Trump had taken huge steps toward securing their respective parties’ nominations.

The picture is clearest on the Democratic side, where the Clinton campaign successfully derailed the Bernie Sanders Express, which roared out of Michigan last week. Her easy victories in Florida and North Carolina had been expected, but in defeating Sanders handily in Ohio—her margin of victory was more than ten points—and also coming out narrowly ahead in Illinois and Missouri, where Sanders had been campaigning hard, Clinton surprised even some of her own supporters.

In so doing, she confirmed some things that had been called into question: she can win big states outside the South, she can win in the Midwest, and, at least in some places, she can attract almost as many white voters as Sanders. In Ohio, exit polls showed that she had the support of fifty-three per cent of white voters and sixty-seven per cent of black voters. Among white women, she got sixty-one per cent. As long as she can split the white vote and win the non-white vote by large margins, she can’t be beaten.

After Tuesday’s sweep of five states, the former Secretary of State has a lead of more than three hundred delegates, and that isn’t counting the Party-appointed superdelegates, the vast majority of whom are on her side. The Sanders campaign has the resources and the enthusiasm to carry the fight all the way to the convention, but it no longer has an obvious route to victory. To overtake Clinton, the Vermont senator would need to rack up huge victories in states like New York and California. That’s not impossible, but it helps to explain why Predictwise, a Web site that combines information from the betting markets and the polls, now puts the probability of Clinton clinching the nomination at ninety-four per cent.

When the networks called the Ohio race, shortly before nine o’clock, the Clinton campaign headquarters, in Brooklyn, erupted in cheers. A few minutes later, Clinton addressed a large crowd of supporters gathered at the West Palm Beach Convention Center. After praising Sanders for running “a vigorous campaign,” she turned her attention to Trump, trying out some of the attack lines we will probably be hearing again in the months ahead. “Our Commander-in-Chief has to be able to defend our country, not embarrass it,” Clinton said. “When he embraces torture, that doesn’t make him strong. It makes him wrong.”

As of early Wednesday, Predictwise had the probability of Trump getting the G.O.P. nomination at seventy-eight per cent. That estimate might well be low, despite John Kasich’s victory in his home state, Ohio. In beating Marco Rubio by nineteen percentage points in Florida, then following up that triumph with narrower wins in Illinois and North Carolina, and prevailing in a squeaker in Missouri, Trump added more than a hundred and fifty delegates to his tally, widening his lead over Ted Cruz to more than two hundred.

On paper, thanks to Kasich’s victory in Ohio, a winner-take-all state with sixty-six delegates, the electoral math still looks tricky for Trump. To reach the twelve hundred and thirty-seven delegates required for a majority, he would need to take fifty-nine per cent of the remaining delegates, which is a big challenge. But, even if he comes up a bit short, he will probably get the nomination. For anything else to happen, there would have to be a brokered convention at which Republican Party bigwigs somehow seized the nomination from Trump. Although this scenario has received a lot of attention recently, it is highly unlikely.

Why? On Tuesday, Trump won his sixteenth, seventeenth, eighteenth, and nineteenth states. Ted Cruz has won seven. Rubio, who confirmed that he was ending his candidacy, won a single state, Minnesota. Now Kasich has a state in his column, too. In the coming weeks, as the race moves to the East and West Coasts, Trump looks set to rack up more victories. Eventually, the Republican Party will be confronted by a question that David Axelrod, President Obama’s former campaign manager, posed on CNN: “How do you deny someone who has come close to twelve hundred thirty-seven, and won all over the country?”

Despite the machinations of the Never Trump movement, the answer, surely, is that the anti-Trump Republicans can’t deny Trump—not forever. It is still theoretically possible for Republican voters in the remaining states to unite behind Cruz or Kasich (who, in an interview with CNN, described himself as “the little engine who could”), but the more likely outcome is that Trump gets the nomination and the Weekly Standard/National Review crowd, who oppose him, persuade a more orthodox conservative to run on a third-party ticket. But, even in that case, Trump would be the official Republican Party candidate.

At about ten o’clock, shortly after the networks called North Carolina for him, Trump appeared onstage in Palm Beach and delivered an even wackier performance than usual. With his campaign manager, Corey Lewandowski, who stands accused of manhandling a female reporter, standing next to him, Trump spent as much time thanking the voters and politicians of the Mariana Islands, which had contributed a mere nine delegates to his cause that morning, as he did thanking the voters of Florida, Illinois, and North Carolina, who among them had contributed a hundred and fifty-two. He pointed out how far he had come since starting out, last July, and, interestingly, appeared to give the Islamic State of Iraq and al-Sham much of the credit for his rise. The terrorist attacks in Paris happened, he said, and his campaign “took on a whole new meaning.” Americans were looking for security, “and all of a sudden the poll numbers shot up.”

Perhaps Trump was tired, or perhaps he just couldn’t be bothered, but he didn’t deliver his usual peroration about the evils of Hillary Clinton and how badly he was going to beat her in the general election. Nor did he address the febrile atmosphere at his campaign rallies or the demonstrations against him. Instead, he complained about all the negative advertising that had been directed at him in Florida, and described how it had disrupted a golf tournament he attended a couple weeks ago at one of his courses, Trump National Doral. Then he told the crowd what he had learned about political campaigning: “There’s nothing like it: lies, deceit, viciousness . . . disgusting reporters.”

Should Trump be confirmed as the G.O.P. Presidential nominee, we can expect more lies, more deceit, and more viciousness. Unless something very unexpected happens, it will be up to Hillary Clinton to keep him out of the White House.