Trump seized on the shooting deaths of the officers in Baton Rouge to bolster his case that he is the better candidate in the Nov. 8 U.S. presidential election to restore law and order than his rival, Democrat Hillary Clinton.
"We grieve for the officers killed in Baton Rouge today. How many law enforcement and people have to die because of a lack of leadership in our country? We demand law and order."
Clinton had no immediate comment on the latest violence.
There were no plans to delay Monday's start of the four-day Cleveland convention, where thousands of Republican delegates are gathering amid a threat of protests both for and against Trump, 70, a businessman-turned-candidate.
Security was extraordinarily tight with downtown streets lined by concrete traffic dividers and tall metal fences, propelled by a new urgency after an attacker drove his truck into a holiday crowd in Nice, France, last week, killing 84 people.
After Sunday's shootings in Baton Rouge, in which three other police officers were wounded, the head of Cleveland's police union asked Ohio Governor John Kasich to suspend state laws allowing people to openly carry firearms, but Kasich said he lacked the authority to do so.
It was not immediately clear there was a link between Sunday's shootings and recent unrest countrywide over police killings of black men, one of them a shooting in Baton Rouge less than two weeks ago.
Despite a lack of clarity about the motive and specifics of Sunday's incident, Trump sought to link the violence to the U.S.-led fight against Islamic State, writing: "We are TRYING to fight ISIS, and now our own people are killing our police. Our country is divided and out of control. The world is watching."
Trump enters the crucial week trailing Clinton in most national opinion polls and needs a bounce from the convention to vault him into a more competitive position.
Republican strategist Hogan Gidley said the violence gave relevance to Trump's message.
"It's something that Donald Trump and his crowd were already prepared to talk about," he said. "This is an epidemic in this country now and we've got to solve it."
NIXON IN 1968
Democratic strategist David Axelrod tweeted that Trump's effort to make himself a law-and-order candidate reminded him of a similar attempt by Richard Nixon in 1968, when the Republican won his first presidential election.
"Someone's been studying '68," Axelrod tweeted.
Trump's goal at the convention is to get more American voters to take a fresh look at him and, he hopes, to see him in a more favorable light, after his victory over 16 other Republican candidates in a brutal battle marked by insults and inflammatory rhetoric that left many in the party divided.
To that end, many speakers will talk about their views on Trump, from daughter Ivanka to women's pro golfer Natalie Gulbis."It's going to be a very personal convention. I mean, you’re going to have his family speaking. You're going to have friends who have known him speaking," Trump campaign manager Paul Manafort told CBS's "Face the Nation."
Many longtime party fixtures are staying away from Cleveland.
Republican National Committee Chairman Reince Priebus, who has been a private counselor to Trump, said Trump is now pivoting slowly to the general election and the convention will help.
"He's never run for anything before. ... I think it's just taken longer to pivot, and I think he's pivoting," Priebus told NBC's "Meet the Press."
The convention will also provide Republican faithful with their first look at his vice presidential running mate, Indiana Governor Mike Pence, who was announced on Saturday after a messy selection process.
Hoping to win over more traditional Republicans, Trump picked the social conservative Pence over two other finalists, former House of Representatives Speaker Newt Gingrich and New Jersey Governor Chris Christie.
Trump's coronation in Cleveland will come on Thursday. "His convention speech will be the most important moment of the campaign and the largest television audience that has ever watched him," Republican strategist Matt Mackowiak said.
"The stakes could not be higher. I expect it to be a prepared speech that is very well-developed, with poll-tested language for maximum effect. He only has one chance to deliver his nominating speech."
The disorganized nature of the running mate rollout - in which Trump failed to fully project the power of the partnership - had some Republicans worried that they could see more of the same at Cleveland.
"As a master entertainer, Trump knows that he’ll have to be much more direct with his messaging and needs to tighten up his delivery when the convention begins," said Republican strategist Ron Bonjean.
(Additional reporting by Kim Palmer; Editing by Howard Goller)
