Cleveland - Stubbornly undercutting calls for Republican unity, Texas Senator Ted Cruz refused to endorse Donald Trump on Wednesday night as he addressed the GOP convention, ignoring thunderous boos from furious delegates as he encouraged Americans to simply "vote your conscience" in November.In a surreal moment, Trump unexpectedly walked into the arena just as Cruz was wrapping up his remarks. Delegates chanted Trump's name and implored Cruz to voice his support for the businessman, to no avail."Vote for candidates up and down the ticket who you trust to defend our freedom and to be faithful to the Constitution," Cruz said. While he backed some of Trump's policy proposals, including building a wall along the US-Mexico border, he mentioned the GOP nominee by name only once.Cruz's defiance ripped open party divisions anew, on the summer's biggest political stage. Trump allies were infuriated, including New Jersey Governor Chris Christie, who said Cruz's decision was "totally selfish".Pence debutThe stunning moment upended what was shaping up to be the convention's most successful night, and overshadowed Indiana Governor Mike Pence's national convention debut as Trump's running mate."You have nominated a man for president who never quits," Pence said. "Until now, he's had to do it all by himself against all odds but this week, with this united party, he's got backup."Trump's campaign had hoped Pence's address would quiet Republican doubts about Trump. Unlike Trump, Pence is an experienced politician, favorite of conservatives and ally of party leaders.Taking the stage shortly after Cruz, former House Speaker Newt Gingrich tried to explain away the senator's lack of support for the nominee."Ted Cruz said you can vote your conscience for anyone who will uphold the Constitution," he said. "In this election there is only one candidate who will uphold the Constitution."It was unclear why Trump's campaign invited Cruz to speak — in a headlining role, no less — without getting him to agree to an endorsement. The decision was sure to spark a new round of second guessing about the campaign's management of the convention and preparedness for a bruising general election against Democrat Hillary Clinton.Trump did get a boost from Wisconsin Governor Scott Walker, one of the 16 Republicans whose White House dreams were vanquished during the primary. Still, Walker suggested he was driven as much by a desire to keep Clinton out of the White House as admiration for his party's nominee."Let me be clear: a vote for anyone other than Donald Trump in November is a vote for Hillary Clinton," Walker said.Dancing in the aislesAfter two nights of low-energy speeches, the crowd packed into the arena was noticeably more energetic on Wednesday night, dancing in the aisles and waving signs reading, "America Deserves Better Than Hillary."Lynne Patton, a longtime Trump employee, spoke movingly about the businessman's strong family. Patton, who is black, said she was proud to support Trump "not just in spite of the colour of my skin, but in fact because of the colour of my skin."Trump's campaign had hoped that by the convention's end, voters would look past the gathering's rough start, including the plagiarism charge involving Melania Trump's opening address. After 36 hours of denials, the campaign moved to put the matter to rest Wednesday, releasing a statement from a speechwriter who took blame for including lines from a Michelle Obama speech in the remarks.Trump, who will address the convention Thursday night, cheered on the night's proceedings via Twitter. After Walker's remarks, Trump wrote, "Great speech!"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.In his convention address, Cruz spoke at length about the recent stretch of violence across the country. He urged Americans to fight for the families of five police officers killed in his hometown of Dallas, as well as the family of Alton Sterling, a black man killed by police in Louisiana.Attacks on ClintonWhile Trump has dominated campaign coverage for months, Clinton has been the negative star of the GOP convention. Speakers have painted an apocalyptic vision of America if she should win and have aggressively challenged her character. While Clinton has been a target of GOP ire for decades, the harshness of the attacks has been striking.For a third straight night, the crowd repeatedly chanted, "Lock her up." While anti-Clinton sentiment is an easy way to bring Republicans together, the negativity crossed the line for some in the party."Certainly races can be won based on focusing on the opponent," said Senator 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."Wednesday afternoon, Pence and his family, along with Trump's adult children, greeted the billionaire as his helicopter landed by Cleveland's picturesque lakefront.Eric Trump, the candidate's 32-year-old son, took the stage near the evening's end, praising his father as other family members had earlier in the week."Vote for the one candidate who does not need this job," he said.