By Ginger Gibson and Emily Stephenson
CLEVELAND (Reuters) - The Republican National Convention briefly erupted in chaos on Monday when opponents of presumptive U.S. presidential nominee Donald Trump stormed out of the room and others chanted in a failed attempt to force a vote opposing his candidacy.
The turmoil threatened efforts by the Trump campaign to show the party had united behind the businessman-turned-politician and distracted from the day's theme of "Make America Safe Again," meant to depict Trump as a strong leader capable of shielding the country from violence.
The convention's opening night featured a string of emotional speakers attacking Democratic presidential candidate Hillary Clinton's record as secretary of state under President Barack Obama, arguing she had made Americans vulnerable to Islamist militancy.
"I blame Hillary Clinton personally for the death of my son," said Pat Smith, the mother of an information management officer who was among the four Americans killed in an attack on a U.S. mission in Benghazi, Libya, in 2012.
Television actor Scott Baio said Clinton wanted to continue the policies that were "wrecking this country." In a play on Trump's campaign slogan, he added: "So let's not just make America great again, let's make America ... America again!"
The anti-Trump forces interrupted the proceedings earlier in the day, seeking to change the party's nominating rules to allow delegates to support alternative Republican candidates over Trump.
Party leaders held a voice vote, then declared the opponents lacked enough support, triggering pandemonium on the floor of the Cleveland basketball arena where Trump is due to be formally nominated this week for the Nov. 8 election.
Many delegates began chanting: "Roll Call. Roll Call," effectively calling for a lengthy process that would allow every state to weigh in. Some, including the Colorado delegation, walked off the convention floor saying they had to assess their next steps.
"This entire system is rigged to force the vote for Donald Trump," said Kendal Unruh, one of the Colorado delegates.
Ken Cuccinelli, a delegate from Virginia who also favored a roll-call vote, called the situation "appalling".
"This is the party of law and order. ... If you won't obey your own rules there is no reason to think you'll obey any others," Cuccinelli, the state's former attorney general, told MSNBC.
Trump's son and adviser, Donald Trump Jr., threatened the leaders of the attempted revolt, saying: "Your careers are finished" in a message posted on Twitter.
While delivering a jolt to the highly scripted program, the anti-Trump forces failed, their rebellion quashed.
The convention then approved the party policy platform and took a scheduled break before a lineup of evening speakers also due to include Trump's wife, Melania, and former New York Mayor Rudy Giuliani.
But the furor, an embarrassment to Trump, put a spotlight on the deep divisions within the party that have emerged over his candidacy. A string of senior Republicans, worried about Trump's temperament and policies, were already avoiding the convention.
Clinton accuses Trump of lacking the experience and temperament needed to work in the Oval Office. On Monday, Clinton, 68, used an address to a largely black audience to cast Trump as someone who would divide the country along racial, ethnic and religious lines.
KILLINGS OVERSHADOW CONVENTION
The gathering opened on Monday afternoon in the shadow of racially tinged killings of police officers and black men, and as protesters for and against Trump faced off in a plaza a few blocks from the convention, shouting slogans at each other, separated by a wall of police.
Trump allies planned to promote what he has billed as a tough line on law and order and national security in speeches on Monday night.
Sunday's shooting of three policemen in Baton Rouge, Louisiana - a targeted attack that may have been in retaliation for a series of police killings of black Americans - hung over the gathering.
Trump lashed out at Obama, who he said "doesn't have a clue," after the police officers' deaths in Baton Rouge, nearly two weeks after police fatally shot a black man there and after another such death near St. Paul, Minnesota, both of which sparked nationwide protests.
Five policemen were also killed in an ambush in Dallas this month.
Trump has sought to position himself as the law-and-order candidate in an echo of Richard Nixon's successful presidential campaign of 1968.
Iowa's Republican Party chairman, Jeff Kaufmann, said the top issue a month ago for voters in the state was the economy. Now, he said, he was hearing concerns about security.
"Rightly or wrongly, the shootings that we've had have vaulted, not just national security in terms of external terrorism but also the knowledge that terrorism is occurring within our country," Kaufmann said.
Such concerns might lead voters to choose Trump over Democratic candidate Hillary Clinton in November, he said.
(Additional reporting by Emily Stephenson, Amy Tennery, Michelle Conlin, Scott Malone, Daniel Trotta and Jonathan Allen; Writing by Richard Valdmanis; Editing by Howard Goller and Peter Cooney)