Yet under the circumstances Mr Trump’s tally was astonishingly robust. Despite having self-inflicted the worst two weeks of his campaign, and provoking the opposition of almost every senior Republican in Wisconsin, Mr Trump still took more than a third of the vote — and in a state that he was likely to lose.
It is quite possible — even probable — that Mr Trump will fail to win a majority of delegates before the Republican convention in July. But it remains almost inconceivable Mr Cruz will overtake him. The maths are too daunting.
Yet conventional wisdom tends to draw a straight line from whatever happened most recently. In the next two weeks before the far more important New York primary, Mr Cruz will benefit from the “earned media” that will result from his emphatic victory in Wisconsin.
For the time being the momentum is now his. Yet his chances of defeating Mr Trump in New York remain slim.
Wisconsin’s demographics, which skew towards educated conservatives, are similar to that of Iowa, which Mr Cruz won at the start of the primary season two months ago. New York’s are closer to that of New Hampshire, which Mr Trump won handily the following week.
In the next two weeks, Mr Cruz is likely to shift his message to the centre. There will be less talk of God and more talk of empowering women.
It is anybody’s guess what Mr Trump will say, or tweet. His capacity for self-destruction can never be underestimated. But it takes a leap of faith to believe he will be defeated on his home turf by a Texan conservative who denigrates “New York values”.
Wisconsin does not drastically alter the bigger picture. Republicans are probably heading towards a contested convention in Cleveland in which they will confront a choice between Mr Trump and Mr Cruz.
Neither is remotely palatable to the party’s Washington power brokers — to the extent they have anything left to broker. Yet Mr Cruz is considered the less unpalatable of the two.
But he should not delude himself that his newfound allies actually like him — Mr Cruz remains the most detested figure in the US Senate. But his new friends believe that the better he performs against Mr Trump, the more likely the convention will produce a deadlock in which someone more electable, such as Paul Ryan, the Speaker of the House of Representatives, will emerge as a white knight nominee.
That is probably a pipe dream. Between them, Messrs Trump and Cruz will have roughly 80 per cent of the delegates. It would provoke an earthquake, or possibly a riot, to give the nomination to someone else.
John Kasich is the only remaining candidate who could defeat Hillary Clinton in November, according to the polls. But the governor of Ohio has won just one of the contests so far — his own. The pressure on him to drop out and consolidate the anti-Trump vote behind Mr Cruz will only grow.
It is doubtful there is a senior Republican in Washington who would choose Mr Cruz over Mr Kasich — he is their kind of conservative. Yet they are governed by their fears of a Trump nomination. Mr Kasich’s presence can only benefit Mr Trump.
The moral of the story is simple. People celebrate “Wisconsin nice” — and on Tuesday the Midwestern state’s electorate rejected the decidedly not nice Mr Trump.
But what happens in Wisconsin is likely to stay in Wisconsin. Mr Cruz proclaimed it to be a turning point in Wisconsin. In all likelihood it was just another bend in a Republican contest that is meandering steadily towards the Niagara Falls.