(Warning: Some of the following images may be considered graphic.) As Republican candidate Donald Trump's presidential campaign marches forward, protests, unrest and outright violence have at times overshadowed the candidate's message.

This image, taken from video, shows a Trump supporter after a protest on Thursday, April 28, 2016 in Costa Mesa, Calif. Dozens of protesters were mostly peaceful as Trump gave his speech inside the Pacific Amphitheater, but the crowd grew rowdy later in the evening.

Cleveland police are preparing for the possibility of unrest at the Republican National Convention, and some protest groups say they will carry guns. Ohio law permits locals to carry guns openly.

In the lead-up to the convention, local police assembled 2,000 sets of riot gear, 2,000 steel batons, 10,000 sets of flexible handcuffs, bulletproof helmets and pepper spray. Protest groups expected in Cleveland include the New Black Panther Party and Black Lives Matter.

On June 18, 2016, 20-year-old Michael Sandford was arrested at a Trump rally in Las Vegas, Nevada, after allegedly reaching for an officer's gun during the event. According to Secret Service agents, Sandford said he'd planned to kill Trump. He's been charged with an act of violence on restricted grounds. A family friend said he had a history of mental health issues.

A Trump hat is lit on fire on June 2, 2016, during a Trump rally in San Jose, California. Protesters also attacked Trump supporters, burned an American flag and fought with police.

Hundreds protested Trump's rally in San Diego, California, on May 27, 2016, clashing with police and supporters of the Republican presidential candidate. It was one of the largest protests against him. Three dozen people were arrested during the event.

Orange County Sheriff's deputies arrest a protester near the Anaheim Convention Center Wednesday, May 25, 2016, in Anaheim, California.

Republican presidential candidate Donald Trump held a rally at the convention center.

Riot police block off the Albuquerque Convention Center to anti-Trump protests following a rally and speech by Republican presidential candidate Donald Trump at the convention center where the event was held, in Albuquerque, New Mexico, May 24, 2016.

On April 29, 2016, Trump hopped a low barrier to avoid angry protesters at the entrance to the California GOP convention. Some protesters were spotted throwing eggs at riot police and chanting near the hotel where the convention was being held.

Here, Trump smiles as protesters hold up a sign reading "No Place for Hate in Maine" during a campaign rally in Portland on March 3, 2016.

This was the scene on March 11, 2016 outside Peabody Opera House in St. Louis, after a fight between Trump supporters and opponents. This man was reportedly detained by police.

This demonstrator appeared outside of New York's Trump Towers to protest the billionaire's candidacy in September 2015.

Here, Secret Service agents surround Trump during a disturbance as he speaks at Dayton International Airport, March 12.

U.S. Secret Service agents later detained a man after the disturbance in Dayton.

This photo shows Rakeem Jones lying on the ground while being removed by deputies from a Trump rally in Fayetteville, North Carolina.

This photo of Jones was taken after he was allegedly assaulted at the Fayetteville, rally by John Franklin McGraw, 78. Local authorities have charged McGraw with assault and disorderly conduct after he was caught on video hitting Jones at the March 2016 event.

Trump has said he will consider paying McGraw's legal fees, a statement that Democratic presidential candidate Bernie Sanders likened to inciting violence.

At a Feb. 29 campaign event at Radford University in Radford, Virginia, photojournalist Chris Morris got ejected by police and Secret Service after attempting to leave a designated press area to cover Black Lives Matter protesters. The magazine photographer was thrown to the ground in a choke hold.

Trump organizers postponed a planned March rally at the University of Illinois in Chicago after thousands of demonstrators showed up to protest.

Protesters outside the Chicago event even put themselves in the path of a car trying to exit the rally.

A widely circulated video shows this protester in Birmingham, Alabama, being forced to the ground, shoved and kicked by several Trump supporters in November 2015. "Get him the hell out of here," Trump said at the time.

On March 1, 2016, protesters were escorted out of a Trump rally in Louisville, Kentucky. One protester, Shiya Nwanguma, has said she was pushed and shoved at the event; white nationalist Matthew Heimbach has said he participated in the shoving.

This protester interrupted a Trump rally on February 22, 2016 in Las Vegas, Nevada. Another Nevada protester spurred Trump to remark, "I'd like to punch him in the face."

A turban-clad protester was escorted out of a Trump campaign event in Muscatine, Iowa, on January 24, 2016.

At a rally in Vandalia, Ohio, a protester talked back at Secret Service agents after being thrown out of the event.

A protester holds up a sign referring to the Ku Klux Klan during Trump's campaign rally in New Orleans, Louisiana, March 4, 2016.

After protesting at a Trump event in Wichita, Kansas on March 5, 2016, these young Muslims were escorted out of the venue.

This protester interrupted Trump's speech during a campaign rally at the downtown Midland Theater in Kansas City, Missouri, March 12, 2016.