KELLY MCEVERS, HOST:

Donald Trump is defending his campaign manager, Corey Lewandowski. Lewandowski was charged today with misdemeanor battery over an altercation with a reporter earlier this month. Here's what Trump told supporters at a rally in Wisconsin this evening.

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DONALD TRUMP: I have a wonderful guy, a campaign manager. You talk about discipline. And you probably saw what happened today with my campaign - he's a good guy - Corey. And by the way, the easiest thing - Corey, you're fired; I can't do that, can't do it.

MCEVERS: NPR's Sarah McCammon is in Janesville, Wis., at the site of that Trump rally. And Sarah, first, remind us about this incident that Lewandowski was charged over today.

SARAH MCCAMMON, BYLINE: Well, Kelly, it happened earlier this month in Jupiter, Fla. It was the night of the Michigan and Mississippi primaries. Michelle Fields, a reporter, at the time, for Breitbart News, tried to sidle up to Donald Trump and ask a question, as reporters often do. And afterwards, she said that Corey Lewandowski had grabbed her and nearly pulled her to the ground.

A Washington Post reporter who was there backed up her account. The Trump campaign denied it, and Corey Lewandowski called her delusional in a tweet. So for weeks, there have been, you know, photos and videos of this incident circulating but nothing that was completely clear.

Today though, the Jupiter Police Department released a surveillance video that appears to show Lewandowski reaching out and grabbing Fields. It's the clearest image so far of what happened, and that video was released today along with documents saying that Lewandowski was being charged with misdemeanor battery. He is set to appear in court in May.

MCEVERS: So what has been all the reaction to all of this?

MCCAMMON: The campaign is backing Lewandowski up. They released a statement saying he's absolutely innocent and will plead not guilty. At the rally here today, Trump tried to discredit Michelle Field's story. And members of the crowd really seemed to agree with him, Kelly. They spoke up and nodded and said, you know, that she was a liar and that there was nothing to the story.

He also - Trump also asked if he could charge the reporter because she had, he said, touched him as she was trying to ask the question. So you know, we've also heard, you know, just from some Trump supporters', before the event, skepticism of her version of events.

Now, Trump's opponents, though, have been very critical. Ohio Governor John Kasich at a campaign event in Waukesha, Wis., today said he didn't know exactly what happened, but in a case like this, a staffer of his would have been suspended or fired. Ted Cruz, Texas senator also running for the GOP nomination, accused Trump - Trump's campaign of an abusive culture built on personal insults and physical violence, in Cruz's words.

MCEVERS: There has been some violence at Trump rallies involving protesters. There were big protests that were anticipated there in Wisconsin. Has there been any violence?

MCCAMMON: Today was pretty peaceful. There was a good-sized crowd beforehand outside, but what I saw was fairly calm. Although it was a, you know, a large crowd and lots of police at these events. I'm seeing more and more of them, it seems like, as time goes by. But you know, there was a woman with a baby and a guy with a guitar, so it was all pretty relaxed - people holding signs that said, stop Trump and, no wall.

MCEVERS: Trump is the undisputed frontrunner in the Republican race, but next week's primary there in Wisconsin is looking pretty competitive between him and Ted Cruz. What did he have to say to the crowd there in Janesville?

MCCAMMON: Well, he criticized Wisconsin Governor Scott Walker who endorsed Ted Cruz this morning. And also House Speaker Paul Ryan came up. In both cases, amazingly, the crowd booed both of those men who are, you know, major Republican figures here in Wisconsin. Even Trump seemed surprised when the crowd booed Ryan. But you know, Trump's been largely off the campaign trail since the March 15 primaries. He's here all week. So is Ted Cruz with that primary just about a week away.

MCEVERS: NPR's Sarah McCammon on the campaign trail in Wisconsin. Thank you.

MCCAMMON: Thank you. Transcript provided by NPR, Copyright NPR.