Donald Trump's campaign manager Corey Lewandowski has been charged with battery over his alleged manhandling of a female reporter earlier in March, US media reported Tuesday.
Also Tuesday, former Republican presidential candidate Scott Walker came out in support of Ted Cruz.
The charges against Lewandowski were brought by police in Jupiter, Florida, where the incident occurred. Former Breitbart reporter Michelle Fields accused Lewandowski of roughly pulling her away as she approached Trump at a campaign event.
A spokeswoman for Trump's campaign said that Lewandowski was absolutely innocent, and looked forward to his day in court.
Trump himself took to Twitter to defend his campaign manager: "Wow, Corey Lewandowski, my campaign manager and a very decent man, was just charged with assaulting a reporter. Look at tapes - nothing there!"
Surveillance camera video of the incident appears to show Lewandowski grabbing the reporter's arm.
Speaking to reporters later, Trump said Lewandowski had been "seriously maligned" and that "no jury would convict a man" for the actions shown in the video.
In Florida a simple battery conviction can lead to up to a year in prison or a fine.
Trump's opponents in the Republican race were unsparing in their responses.
Cruz, a senator from Texas, said the news was "a consequence of the ... the abusive culture" surrounding the Trump campaign.
Ohio Governor John Kasich called Lewandowski's actions "totally and completely inappropriate," and said he would either have suspended or fired him.
Democrat Hillary Clinton, while not speaking directly to the charges, said that the front-runner had been inciting violence at his rallies and that "ultimately the responsibility is Mr Trump's."
Meanwhile, a week before the Republican primary in his state, Wisconsin Governor Walker endorsed Cruz as "a principled, constitutional conservative who can win."
Writing on Twitter, Walker said, "@TedCruz is the best-positioned candidate to both win the Republican nomination and defeat Hillary Clinton. I'm proud to stand with him."
Walker, who was considered a strong contender at the outset of a Republican race crowded with 17 candidates, ended his run in September after low poll numbers.