Donald Trump signs RNC loyalty pledge (19 images)

A security guard and protester get into a scuffle when a protest takes place outside of Trump Tower after Republican Candidate for President of the United States Donald Trump speaks at a press conference at Trump Tower in New York City on September 3, 2015. U.S. presidential hopeful Donald Trump on Thursday signed a pledge not to run as an independent candidate if he loses the Republican Party nomination. Photo by John Angelillo/UPI

A security guard and protester get into a scuffle when a protest takes place outside of Trump Tower after Republican Candidate for President of the United States Donald Trump speaks at a press conference at Trump Tower in New York City on September 3, 2015. U.S. presidential hopeful Donald Trump on Thursday signed a pledge not to run as an independent candidate if he loses the Republican Party nomination. Photo by John Angelillo/UPI

Protesters dressed in KKK cloths stages a protest outside of Trump Tower after Republican Candidate for President of the United States Donald Trump speaks at a press conference at Trump Tower in New York City on September 3, 2015. U.S. presidential hopeful Donald Trump on Thursday signed a pledge not to run as an independent candidate if he loses the Republican Party nomination. Photo by John Angelillo/UPI

Protesters dressed in KKK cloths stages a protest outside of Trump Tower after Republican Candidate for President of the United States Donald Trump speaks at a press conference at Trump Tower in New York City on September 3, 2015. U.S. presidential hopeful Donald Trump on Thursday signed a pledge not to run as an independent candidate if he loses the Republican Party nomination. Photo by John Angelillo/UPI