Donald TrumpDonald John TrumpMichael Cohen: I pray Michelle Obama's words will unite country again Michelle Obama: ‘I stopped even trying to smile’ during Trump’s inauguration Trump wants to end federal relief money for Puerto Rico: report MORE called into Bill O'Reilly's Fox News show on the first night of the GOP convention.

Trump's call came during a speech by Pat Smith, the mother of Sean Smith, one of four Americans killed in the Benghazi, Libya attack. 

MSNBC and CNN carried Smith's remarks live to the crowd, but Fox cut to its interview with Trump. 

During the interview, the presumptive GOP presidential nominee previewed his Thursday speech where he will accept his party's nomination. 

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The businessman promised a fairly long speech with “many themes — one of them is law and order,” he told O’Reilly. 

At the top, the Fox News host asked Trump if he’ll make the killing of police officers — a topic in the spotlight after the Sunday shooting of six officers in Baton Rouge, La. — a focus of his campaign.

“Of course. It’s a big issue; it’s a horrible issue; and it’s going to be a very important one. It’s called law and order. We want law and order,” Trump said. 

Asked about the Black Lives Matter movement, Trump said some protesters are “essentially calling death to the police, and that’s unacceptable.” 

He said if elected president, he’d “look into it very seriously,” and when pressed on what that would mean, said he would “perhaps talk with the attorney general about it or do something, but at a minimum we’re going to have to be watching.” 

Trump will speak from Cleveland on Monday night for what he promised would be a “very, very short” introduction of his wife, Melania Trump, who is the first headliner of the convention.