Ted Cruz won't be the Republican presidential nominee, but on Friday he promised to hold Donald Trump's feet to the fire on the GOP platform, particularly over conservative fears the billionaire businessman might soften language opposing abortion.

Speaking to conservative Oklahoma radio host Pat Campbell, the Texas senator vowed not to let the former reality television star "screw around with the party platform and remove the abortion plank, or alter it."

"You have my word," he said. "One of the reasons that we are continuing to work to elect conservatives to be delegates, even though Donald has the delegates to get the nomination, we intend to do everything we can to fight for conservative principles to prevent Washington forces from watering down the platform."

Asked by Campbell if he would be able support Trump or if he thought Trump would meet his standards of conservatism, Cruz said: "I hope that he will."

"I hope we have a nominee that will actually defend conservative principles," he said.

Cruz, who ended his bid for the White House earlier this month after being "clobbered" by Trump in Indiana, blamed the media for the defeat, whom he said paid too little attention to his primary wins and predicted a major Trump victory in New York.

"There was a period in the race where we had won five states in a row in just over three weeks … [in] landslide victories," he said. But instead of covering Cruz's wins, the media "began saying over and over, is well, the New York primary is coming, and then what proceeded to happen: We actually saw our numbers drop through the floor the week before the New York primary."

"That had the effect within 48 hours of our numbers plummeting 20 points," he continued. "Our supporters were told nonstop by the media that it was hopeless, that there was no way to win, and they eventually gave up and I said, 'Alright, well, if [Trump is] going to be the nominee, I surrender.'"

It is be impossible to say what kind of impact the wall-to-wall coverage of Trump had on the race; an analysis by SMG Delta estimates Trump got $2 billion in free media during the GOP primary.