Stakes Rising for Trump's RNC Speech After Cruz Performance

CLEVELAND -- With Ted Cruz's jaw-dropping speech on Day 3 of the Republican National Convention dominating the conversation today, the bar is rising for Donald Trump's address this evening.

"The pressure is on Trump tonight, big time," James Campbell, a political science professor at the University at Buffalo in New York, told ABC News this morning.

"He needs a big bump coming out of this convention and too many things have gone wrong so far. The only way to salvage this is a blockbuster speech."

Trump campaign chairman Paul Manafort told ABC News this morning that while he believes the Texas senator's decision not to endorse Trump on stage Wednesday is "a losing model," the point of the Cleveland convention itself goes beyond anything that involves Trump's former foes.

"His goal with this convention was, among other things, to unite the party," Manafort said of Trump.

But another goal is to show the U.S. people that Trump can lead. Going into the convention, the latest ABC News-Washington Post poll, from July 17, found that 60 percent of respondents said they did not believe that Trump is qualified to be president.

Beyond that, the poll had Trump's unfavorability rating at 64 percent.

Campbell, who has written the upcoming book "Polarized: Making Sense of a Divided America," said Trump's speech tonight "must do what he can to undo the damage of his nomination campaign."

"This is a tall order. I'm not sure any speech can do that and I'm not even sure Trump understands that this needs to be done," Campbell said.

As for Trump, Wednesday night's Cruz address seems to be attracting as much of his attention as speech prep.

He posted a series of tweets this morning bashing his former rival.

Trump will be the closing speaker of tonight's program and will be taking the stage after his eldest daughter, Ivanka, introduces him.