JACKSON, Miss. (WJTV) — Mississippi Congressman Bennie Thompson sent a letter to Homeland Security Thursday addressing his concerns about violence that could occur if Republican Nominee Donald Trump does not win the upcoming general election.

He sent the letter to Secretary Jeh Johnson of the Department of Homeland Security.

Thompson, a Democrat who represents the second congressional district of the Magnolia state, said antigovernment militia groups grew by one-third last year. He said since the some of their ideas have become more mainstream, he said it could fuel violence.

He also said that Trump’s comments claiming that the election is rigged could also fuel extremist groups. Thompson said some Trump supports have already raised the possibility of a civil war or a race war if Trump loses.

Thompson is also a ranking member of the Committee for Homeland Security.Read Thompson’s full letter here.