There have been back-to-back attempts on former President Donald Trump's life in the last two months.Gene J. Puskar/AP PhotoFormer President Donald Trump has survived two assassination attempts in as many months.Political threats and violence are surging, and an expert on terrorism thinks it will get worse.Trump is a particular lightning rod for violence among both supporters and detractors.Amid a contentious race for president, the nation has seen a surge in brutal rhetoric online, increasing threats, and two attempts to assassinate a major party's candidate.