Cole Tomas Allen, the suspect in the attempted White House Correspondents’ Dinner shooting, is unusual among attempted assassins — in his normalcy. His political grievances, laid out in a manifesto and social media posts, are not dissimilar from those of an ordinary Democrat. He believed that President Donald Trump was a lawless, corrupt leader who abused immigrants, perpetrated war crimes, and presented an existential threat to American democracy. Key takeaways I spoke with five leading experts on political violence in the United States. The picture they painted was complicated; they often didn’t agree on key points. But my best read of the evidence they presented led me to three conclusions. Political violence becomes more likely when people believe that politics takes on existential stakes — that their way of life or cherished values are at risk — and that there is no hope of peaceful resolution to their conflicts.…