CLEVELAND -- Straining to shore up Republican unity, Indiana Gov. Mike Pence will urge conservatives to shed their unease about Donald Trump Wednesday night as he makes his national convention debut as the businessman's running mate.

But much of the attention will be on Texas Sen. Ted Cruz, a favourite of the right who has yet to endorse Trump.

The gulf between Pence's hearty embrace of Trump and Cruz's reluctance was emblematic of the turmoil still roiling the GOP. A day after Trump formally became the presidential nominee, some delegates at state gatherings around Cleveland were still struggling to come to terms with their unorthodox new standard-bearer.

Iowa delegate Cecil Stinemetz called Trump "the worst nominee that we have put forward for the Republican Party in the history of the Republican Party" and said he didn't plan to return to the convention floor the rest of the week.

Republican worries about Trump's preparedness for a general election battle with Democrat Hillary Clinton have only been reinforced during the convention. The campaign struggled to respond to plagiarism charges involving Melania Trump's Monday night address, finally releasing a statement Wednesday from a speechwriter who took blame for including lines from a Michelle Obama speech in the remarks.

Campaign officials see Pence's address as an important opportunity to reassure the doubters. In a show of unity, he'll be introduced by House Speaker Paul Ryan, a lukewarm Trump supporter, and lay out his reasons for partnering with the celebrity businessman who is in many ways his opposite.

While Pence is expected to make the case that Democrat Hillary Clinton is unfit for the White House, officials said his speech will not be a full-throated takedown in the style of earlier speakers.

Cruz was harshly critical of Trump in the waning weeks of their primary battle, calling the businessman a "pathological liar" and "utterly amoral." He arrived in Cleveland with an eye on his own political future, holding a rally with hundreds of supporters who greeted him with chants of "2020" -- suggesting Cruz's backers have no interest in seeing Trump become a two-term president.

Cruz was expected to continue sidestepping a formal endorsement of Trump during his convention remarks. Top Trump aide Paul Manafort said the senator would at least "suggest" he is backing the nominee, while other Republicans said Cruz would argue the importance of keeping Clinton out of the White House.

That message is sure to be well-received in the convention hall, where Clinton has been under constant attack. Speakers have painted an apocalyptic vision of America if she wins and have aggressively challenged her character. While Clinton has been a target of GOP ire for decades, the harshness of the attacks was still striking.

Former GOP presidential candidate Ben Carson connected Clinton with Lucifer. New Jersey Gov. Chris Christie implored delegates to shout "Guilty!" in response to various accusations of wrongdoing. And for a third straight night, the crowd filling the convention hall Wednesday chanted, "Lock her up."

For at least some delegates, the negativity crossed a line.

"Certainly races can be won based on focusing on the opponent," said Sen. Bob Corker of Tennessee. "But I think we're at a place in our country's evolution where it's particularly important now, with all that's happened and the concerns that people have, for a positive vision to be laid out."

Trump has shown little concern for maintaining any modicum of political decorum. Yet Pence, the Indiana governor and Trump's new political partner, has spoken out against negative campaigning and was put on the Republican ticket in part to provide a temperamental contrast.

The Trump-Pence ticket was off to an awkward start, with some Republicans whispering that the businessman was gripped by last-minute doubts about his pick.

The campaign hoped for better imagery Wednesday. Pence and his family, along with Trump's adult children, greeted the billionaire as his helicopter landed by Cleveland's picturesque lakefront.

"What begins in Cleveland will end in the White House, I'm convinced," Pence declared as they greeted a small group of supporters.

Former House Speaker Newt Gingrich, who had been a top vice-presidential contender, was also scheduled to address the convention. Two of Trump's other vanquished primary rivals -- Wisconsin Gov. Scott Walker and Florida Sen. Marco Rubio -- were also speaking, the latter via video.

Trump's family will also continue efforts to show a softer, more personal side of the real estate mogul. At least one family member was scheduled to speak each night of the convention, with 32-year-old Eric Trump taking the stage Wednesday.

Mrs. Trump was the first in the family to address the convention, warmly casting her husband as kind and loyal. But her speech was quickly subsumed by the plagiarism charges, overshadowing nearly all of the campaign's other messaging.

After the campaign spent 36 hours dismissing the dustup as absurd -- and any similarities with Mrs. Obama's speech as coincidence -- writer Meredith McIver said Wednesday she had included passages from the first lady in Mrs. Trump's address. McIver said she offered her resignation over the incident, but Trump rejected it.

Trump embraced the swirling attention.

"Good news is Melania's speech got more publicity than any in the history of politics especially if you believe that all press is good press!" Trump said on Twitter.

AP writers Jonathan Lemire, Kathleen Hennessey and Steve Peoples in Cleveland, Barbara Rodriguez in Des Moines, Iowa, John Hanna in Topeka, Kansas, and Meg Kinnard in Columbia, South Carolina, contributed to this report.