As this "Poll of all Polls aggregate graph to March 29th from Huffington Post Pollster shows Ted Cruz (and Kasich) where both in a sharply ascending mode after all the other competitors, especially Marco Rubio had dropped out.
Donald Trump had peaked and his trend line had commenced a downwards turn. This was an absolutely crucial time in the campaign for Cruz with his competitors mostly gone and Wisconsin coming up for him ahead of the less promising eastern states.
Then on April 2nd the graph for Trump turned upwards in a sharply accelerating line and gained almost ten points from 43.2% to 53.1% in the latest May 1st poll where the campaign ended
What can be the reason for this striking change for Trump and decline for Cruz at what was a crucial time for both? The answer seems, clearly to be the public's perception of the manifestly unfair 'stealing of delegates at the Colorado Caucuses which commenced, hardly coincidentally on April 2nd and ran, in the glare of nationwide publicity, to April 9th:
"TRUMP ERUPTS AS CRUZ SWEEPS COLORADO WITHOUT VOTES
'Biggest story in politics. This will not be allowed!'
Republican presidential front-runner Donald Trump erupted on “Fox & Friends” Monday morning after a weekend that saw Sen. Ted Cruz of Texas sweep all of Colorado’s 34 delegates without any votes being cast by citizens in a traditional primary process.
“I’ve gotten millions … of more votes than [Sen. Ted] Cruz, and I’ve gotten hundreds of delegates more, and we keep fighting, fighting, fighting, and then you have a Colorado where they just get all of these delegates, and it’s not [even] a system,” Trump said, during the Fox News broadcast. “There was no voting. I didn’t go out there to make a speech or anything. There’s no voting.”
His comments came after Cruz won the remaining 13 delegates at the weekend’s convention, bringing his total for the state to 34, an outcome he described as unfair and just shy of illegal.
The Wisconsin primary took place during the period of the Colorado caucuses (April 5th) and this too turned out to be a Pyrrhic victory for Cruz. It was a substantial win but, again, it seemed to be tainted by an in the tank Wisconsin establishment, and the local media/talk back radio being not only vociferously but in appearance manifestly biased against Trump and rude to his emissary Sarah Palin, who's dignity in face of a hostile audience added further bad optics for Cruz.
When the Colorado machine finished assigning all the delegates to Cruz in the midst of protests and a visibly angered Trump, and all his previous warnings about "Cruz stealing the election" seem not only justified but manifestly so.
Exit polls made it clear that the absolute majority of Republican voters wanted the person who won the most votes to be the nominee. That the Cruz team was perceived, rightly, as going against that wish by picking off Trump's delegates so they could turn to Cruz on a second ballot clearly turned voters against
This was illustrated emphatically in the next 7 primaries where Cruz was destroyed in state after state and which culminated in his campaign finishing in Indiana. In the end Cruz lost through winning, his major, tainted, victories in Iowa and Wisconsin turned out to be champagne from a poisoned chalice
