Trump is speaking at a rally in Portland, Maine.
"There is no scenario in which Mexico will pay for" the wall, Luis Videgaray said.
"I think he’s being fed this, probably promised a lot of money," the Fox News host said.
Romney will reportedly call Trump "a phony, a fraud" in the speech.
"He would leave — and he'd have a right to leave," Graham said.
“We have no plans to get involved in the primary," a spokesman said.
Trump is expected to increase his delegate lead through Super Tuesday.
The victory helps Cruz position himself as the viable alternative to Trump.
Trump was declared the winner in Massachusetts, Tennessee and Alabama.
The billionaire has picked up a win in Georgia to start the night.