Cruz victory sets the scene for backroom bid to dump Trump
Republicans are eyeing the prospect of a rare contested convention at which a "white horse" candidate could emerge as the party's presidential nominee, after Ted Cruz's resounding defeat of Donald Trump in Wisconsin.
Mr Cruz's victory cuts Mr Trump's chances of gaining enough primary election delegates to clinch the nomination, but the Texas senator has no realistic path to win a majority himself.
The party establishment is therefore hoping to parachute Paul Ryan, the Speaker of the House, into the nomination at July's convention.
If no contender gains an outright majority, even someone who had not declared as a candidate can be nominated as the convention turns into a scramble for the delegates' votes.
The party elite sees Mr Ryan - Mitt Romney's 2012 running mate - as well positioned to triumph.
Scott Walker, the Wisconsin governor, said Tuesday's result made a contested convention "very likely".
He has backed Mr Cruz, but has been forced to deny claims that he aims to pave the way for an establishment nominee.
While the establishment plot is being hatched in backrooms, the battle between Mr Trump and Mr Cruz is far more public.
The property tycoon offered condemnation rather than congratulations after the Wisconsin result.
"Ted Cruz is worse than a puppet - he is a Trojan horse, being used by the party bosses attempting to steal the nomination," the Trump campaign said in a statement, with the billionaire uncharacteristically declining to make a speech.
But the anti-Trump movement in the Republican establishment smells blood, which explains Mr Trump's own extraordinarily combative statement.
Mr Trump, seemingly impregnable until a recent catalogue of missteps rendered him suddenly vulnerable, acknowledged as much in his blunt missive - striking in its vituperation, even by his standards. "Donald J Trump withstood the onslaught of the establishment yet again," read his statement.
Fuelling the anger behind such fighting talk was Mr Cruz's margin of victory - sufficiently large to ensure that he won the lion's share of Wisconsin's 42 delegates. The victory makes Mr Trump's task of reaching the magic figure of 1,327 delegates needed to secure the nomination much tougher - and opens the door to a contested convention.
To tie up the nomination before the convention, Mr Trump must now win a much higher proportion of the delegates - 57pc - in the remaining contests than the 48pc he managed in the previous primaries while seemingly all-conquering and cutting a swathe through the Republican field.