CLEVELAND, July 18 (Reuters) - The Republican National Convention erupted in chaos on Monday when some opponents of presumptive U.S. presidential nominee Donald Trump stormed out of the room and chanted in protest at their failure to win a symbolic 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 and Islamist militancy.
The anti-Trump forces wanted to change the party's nominating rules to allow delegates to support alternative Republican candidates over Trump.
When party leaders by acclamation declared the opponents' efforts a failure for lack of votes, pandemonium erupted on the floor of the Cleveland basketball arena where Trump is due to be formally nominated this week.
Many delegates began demanding a roll-call vote, chanting: "Roll Call. Roll Call." Others walked out of the convention floor saying they had to assess their next steps.
KILLINGS OVERSHADOW CONVENTION
The gathering opened on Monday in the shadow of recent racially tinged killings of police officers and black men.
Trump allies will promote what he bills as a tough line on law and order and national security in speeches later in the day.
Sunday's shooting of three policemen in Baton Rouge - a targeted attack that may have been in retaliation for a series of police killings of black Americans - hung over the gathering.
See more of the chaos on the floor:
The theme for the first day of the meeting had already been set as "Make America Safe Again."Trump has sought to position himself as the law-and-order candidate in an echo of Richard Nixon's successful presidential campaign of 1968.
Trump's wife, Melania, was due to speak on Monday night, joined by her husband on stage, as were foreign policy hawk Senator Tom Cotton and retired Lieutenant General Michael Flynn, a national security adviser.
They were likely to promise that Trump will crack down on Islamic State abroad and toughen up on crime at home if he wins the Nov. 8 election.
(Additional reporting by Emily Stephenson, Amy Tennery, Michelle Conlin, Scott Malone, Daniel Trotta and Jonathan Allen; Writing by Alistair Bell; Editing by Caren Bohan and Howard Goller)