IT SEEMS it could really happen, the most viciously personalised, all-round nasty presidential face-off imaginable: Hillary Clinton against her old pal Donald Trump. That was the main takeaway from the big wins the respective Democratic and Republican front-runners scored in five north-eastern primaries, Connecticut, Delaware, Maryland, Pennsylvania and Rhode Island, on April 26th. Because, while both candidates had been expected to do well, and though Mrs Clinton’s grip on the Democratic nomination had already looked secure, the unexpectedly eye-watering totality of Mr Trump’s victories was potentially race-changing. As the Republican contest now swings westwards, for ten last state primaries, the party bigwigs scrabbling to Stop Trump have their work cut out; if he wins in Indiana on May 3rd, Mr Trump may be unstoppable.

To make up the ground he recently lost in Wisconsin—and get back on track for the requisite 1,237 delegates—he was estimated to need a little over 100 of the 118 elected delegates available this week. He won 109, on the back of his biggest wins in terms of vote-share yet. In New York on April 19th he cracked 50% of the vote for the first time; he repeated that feat in all five north-eastern states—winning Rhode Island with 64%, Delaware with 61%. He won almost every county in every state. Ted Cruz and John Kasich were humiliated.

Of the 213 delegates available in the north-eastern quintet and New York, the Texan senator, who has styled himself the only plausible anti-Trump candidate, won just three. Flailing to distract journalists from this meltdown, he declared on April 27th that Carly Fiorina, a failed presidential candidate and businesswoman known for the massive job losses she oversaw at Hewlett-Packard, would be his running-mate. Judged on Ms Fiorina’s performance earlier in the contest, it is as well he may not need her. Mr Kasich’s haul, of nine delegates, was even worse; the Ohio governor had remained in the contest, despite winning only his own state, partly in the hope of doing well with the north-east’s relatively moderate voters.

America's primary agenda: our interactive 2016 election calendar Exit polls in the three biggest states, Connecticut, Maryland and Pennsylvania, offered some familiar explanations for Mr Trump’s success. It was above all fuelled by resentment of the ways in which America’s economy is changing and of the political-business elite presiding over it; more than four in ten Republican voters said Wall Street hurts the economy and Mr Trump won two-thirds of them. Yet the polls also suggested deepening support for Mr Trump, who has now won 26 of the 41 states that have voted, across the Republican electorate. He beat Mr Cruz handsomely among evangelicals and strong conservatives, the Texan’s biggest fans. Given that he also outperformed his poll ratings in every state—reversing a former habit of underperformance—the impression was of a Republican electorate that has, rather suddenly, decided to plump for Trump. There are three possible explanations for this change. One is that voters are unimpressed by the technical hurdles his rivals are trying to pile in Mr Trump’s path. Thus, for example, Mr Cruz’s, impressive effort to insert his supporters onto the lists of delegates that each state will send to the Republican National Convention in July. If Mr Trump failed to win the nomination on a first ballot there, most would be free to vote for the candidate of their choice in subsequent votes, potentially handing Mr Cruz a big advantage. There is nothing underhand about that, yet of course Mr Trump says there is, and opinion polls suggest many might sympathise with him. Most Republicans say their ticket should go to whoever wins the most delegates. A second possible explanation is that Republican voters who strongly disapprove of Mr Trump—around a third of the total—are giving up. The fact that turnout was down on early Republican primaries points to that. A third, related, reason for the pro-Trump wave is that the growing likelihood of Mr Trump as the candidate has sanitised him a bit. Thus, he did better than usual with late deciders—such as Anthony Venditti. “I went in 75% sure I was voting for Cruz,” said the 27-year-old engineer, outside a polling station in Pittsburgh, Pennsylvania. “But I went for Trump because he has the best chance of bringing back manufacturing and jobs.”

The wave could fade. The north-eastern states are packed with the working-class whites who love Mr Trump’s protectionist message best. Indiana, which has 57 delegates available, most of whom the tycoon must win, is more conservative and religious, making it more propitious for Mr Cruz. He is running Mr Trump fairly close; polls put him on 33% to Mr Trump’s 39%. And on April 24th he and Mr Kasich announced a non-aggression pact, under which the governor, who is at 19%, will stop campaigning in Indiana. If more of his supporters were to peel away to Mr Cruz than to Mr Trump, the Texan could win. That is tough to predict; Mr Kasich’s followers dislike Mr Cruz’s caustic conservatism almost as much as Mr Trump’s reckless populism. But it may be their main hope of denying the tycoon the ticket.

In his victory speech—naturally delivered in Trump Tower, in Manhattan—Mr Trump appeared to be readying himself for Mrs Clinton; albeit not in the measured, sophisticated way his advisers have briefed Republican elders to expect. Mr Trump just piled in. “The only card she has is the women’s card,” he sneered—“and the beautiful thing is women don’t like her”. Yet they like him much less—70% of women have a poor opinion of Mr Trump—and this did not seem a good way to woo them.

Mrs Clinton, who won all the north-eastern states except Rhode Island, stretching her lead over Senator Bernie Sanders above 300 elected delegates, was also in general election mode. In her victory speech—delivered in Philadelphia, in recognition of Pennsylvania’s potential importance as a swing state—she beseeched Democrats, independents and even “thoughtful Republicans” to rally to her standard. It would have seemed unimaginable only recently, but the way things are going a few of them might, Even in the most surprising quarters: this week Charles Koch, a billionaire industrialist, libertarian and mega-funder of conservative causes, said it was “possible” Mrs Clinton would make a better president than whoever the Republicans put up.