The conservative campus activist who was assaulted at the University of California-Berkeley has appeared at CPAC on stage with President Donald Trump.

Trump called Hayden Williams up to the stage as he spoke to the cheering crowd at the conservative conference in National Harbor, Maryland on Saturday afternoon.

Williams was tabling for the student group Turning Point USA on February when a man charged up and accused him of 'promoting violence' before socking Williams in the face, in a shocking attack caught on video. A suspect, 28-year-old Zachary Greenberg, was arrested on Friday.

'Do me a favor - sue him!' Trump told Williams onstage at CPAC, as Williams gave a double thumbs-up. 'He's probably got nothing, but sue him forever. Sue the college, the university, and maybe sue the state.'

'He took a hard punch in the face for all of us, remember,' Trump continued. 'And we can never allow that to happen.'

'He's going to be a very wealthy young man. Go get 'em, Hayden,' the President concluded, shaking Williams' hand and embracing the young activist.

Trump called Hayden Williams up to the stage as he spoke to the cheering crowd at the conservative conference in National Harbor, Maryland on Saturday

Trump embraced Williams after praising the young activist, and announced an imminent executive order mandating protections for free speech on college campuses

Williams' surprise appearance tied into Trump's announcement during the more than two hour speech that that he will soon sign an executive order 'requiring colleges and universities to support free speech.'

'If they want our dollars, and we give it to them by the billions, they have to allow ... all people to speak. And if they don't, it will be very costly,' he said.

On Friday, Greenberg was arrested in Berkeley following a 10-day search for the suspect seen attacking Williams on video.

Zachary Greenberg, 28, was charged with assault with a deadly weapon on Friday

He was held on $30,000 bail in Alameda County jail on suspicion of assault with a deadly weapon likely to produce great bodily injury.

He is to be arraigned on Monday at the Wiley W. Manuel Courthouse in Oakland.

Neither Greenberg or Williams are students at the UC-Berkeley.

In a statement to Campus Reform, Williams expressed his view of the news of his attacker's arrest: 'I am grateful to the University of California Berkeley Police Department for its dedication to identifying and arresting the man who attacked me.'

'But while this is a moment for celebration, I remain disappointed by the UC Berkeley Administration, which allowed a culture of intolerance and violence toward conservatives to grow,' he continued.

'I hope UC Berkeley’s leadership will seize on this moment-in-time to take deliberate steps to establish a zero tolerance policy when it comes to violence, and restore Berkeley’s legacy as ‘Home of the Free Speech Movement,' Williams concluded.

Video from the incident shows Williams (left) being confronted by a violent attacker who punched him in the face as he was recruiting for a conservative student group

Williams was running a campus recruitment table for Turning Points USA, a conservative activist group, when he was approached by his attacker in Sproul Plaza.

The sign on the table read 'hate crime hoaxes hurt real victims,' a reference to allegations that actor Jussie Smollett staged a racist and anti-gay attack against himself in Chicago.

Willaims said in an interview with Fox News that a man charged up to the table acting 'erratically' and accused him of 'provoking violence.'

The suspect is heard on video shouting: 'Mother f**ker. You racist little inbred b***h. C**t!'

Williams (left) is seen 'tabling' at UC-Berkley on another occasion last summer

UC-Berkeley campus police said that the attack took place at 3.29pm on Upper Sproul Plaza, and that two men initially approached the table confronting Williams.

'A physical confrontation ensued when one of the two men slapped the phone out of the victim’s hand,' the police statement said.

The attacker then knocked over the table and the two men fought over the phone.

During the incident, the suspect punched the victim several times causing injuries to the eye and nose, police said.

Williams was helping Turning Point USA, but he is not actually a member of the group. Williams is campus representative for Leadership Institute, which runs Campus Reform, the website that first reported on the incident.