For at least 13 minutes Saturday morning, Marco Rubio presented perhaps his most passionate argument yet against GOP presidential frontrunner Donald Trump.

“I still at this moment continue to intend to support the Republican nominee, but it’s getting harder every day,” Rubio said while also strongly criticising the media for promoting Trump.

A day after Trump suddenly canceled a massive Chicago rally amid fights and mass protests, Rubio said the “third-world images” were the result of Trump’s own words.

As Rubio took questions from reporters in Florida, he said:

You saw those images last night of people … often divided up on racial lines in many cases. Police officers bleeding from the head reminiscent of images from the ’60s. I mean, we’re going backwards here. This a frightening, grotesque, and disturbing development in American politics.

Rubio pointed to the fact that Trump often deploys violent rhetoric against demonstrators at rallies. At his events, Trump has mused about punching protesters in the face, and once said he would pay the legal bills of his fans if the assaulted anyone trying to throw tomatoes at him.

“This boiling point that we have now reached has been fed largely by the fact that we have a frontrunner in my party who has fed into language that basically justifies physically assaulting people who disagree with you,” Rubio said.

On Thursday, a Trump rally attendee was reportedly charged with allegedly assaulting a protester who was filmed raising his middle finger to the crowd before being sucker punched. The incident was brought up at Thursday’s primary debate, during which a moderator asked Trump if he was responsible for the “tone” of his rallies.

Trump said he didn’t condone the violence, but the next day in St. Louis, the candidate repeatedly complained about how “gentle” his protesters were being treated. He also suggested that protesters waving their middle fingers should be held responsible for provoking others.

“A Donald Trump supporter sucker punched a man the other day at an event. Donald Trump has yet to condemn it,” Rubio said Saturday.

He continued:

So it tells you, it tells you in many ways he doesn’t want to say anything to his supporters because he doesn’t want to turn them off. Because he understands that the reason why they are voting for him is because he has tapped into this anger. The problem is leadership has never been about taking people’s anger and using it to get them to vote for you. If it is, it’s a dangerous style of leadership.

Rubio, a senator from Florida, has focused his campaign almost exclusively on winning his home state in next Tuesday’s primary contests. During his Saturday press conference, Rubio said he was confident in his chances in Florida, but worried about what a Trump nomination would mean for their party.

“I believe Donald Trump as our nominee is going to shatter and fracture the Republican Party and the conservative movement,” he said.

Watch the press conference below:

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