A gunman was stopped by Secret Service at a White House checkpoint, with no apparent harm to bystanders.

• Shots rang out near the White House while reporters were on camera covering other news.
• Secret Service quickly took the gunman down at the checkpoint.
• The incident happened amid heavy news focus on the Iran situation and US negotiations.
• Reporters on scene had very different reactions, with one barely flinching and another ducking for cover.

Outlook: Expect more details on the shooter's identity and motive in the coming days.