Demonstrators scuffled with police outside the Quicken Loans Arena, preventing some attendees and journalists from entering the convention.
In an interview with Fox News anchor Bill O'Reilly, Trump declares if elected he'll task his attorney general to monitor the group, cofounded by two queer African-American women.
Jesus Retana, a police officer for Dallas's transit system, was one of seven law enforcement officials injured by a sniper on Thursday; five died.
"He was upset about Black Lives Matter," Chief David Brown said, adding that the gunman cited this week's killings of two black men by police in Louisiana and Minnesota.
The morning after the single most deadly attack on law enforcement since 9/11, the mayor and police chief of Dallas and President Obama denounced the deadly ambush.
The chief of police in Dallas says they used a bomb on a robot to kill one of the snipers who opened fire at 11 officers, killing five and wounding at least seven more.
"We don't need sympathy," the pop icon wrote on her website. "We need everyone to respect our lives." Warning: this video contains graphic images.