In the nine years since Donald J. Trump entered American politics, the global perception of the United States has been shaken by the image of a fractured, unpredictable nation. First one, then a second apparent attempt on the former president’s life have accentuated international concerns, raising fears of violent turmoil spiraling toward civil war.

Keir Starmer, the British prime minister, has said he is “very worried” and “deeply troubled” by what the F.B.I. said was an attempt to kill Mr. Trump at his Florida golf course, fewer than 50 days before the presidential election and two months after a bullet bloodied the ear of Mr. Trump during a campaign rally in Pennsylvania.

“Violence has no part to play at all in any political process,” Mr. Starmer said.

Yet, violence has played a core part in this stormy, lurching American political campaign, and not only in the two apparent assassination attempts. There is now widespread concern across the globe that the November election will not end well and that American democracy, once a beacon to the world, has frayed to the breaking point.