Key facts
- President Donald Trump will attend the NATO summit in Turkey on July 7-8.
- U.S. Secretary of State Marco Rubio confirmed Trump's attendance.
- Trump has expressed anger with NATO allies for perceived reluctance to support the U.S. war in Iran.
- Key irritations include allies denying U.S. military bases and naval support.
- Rubio described the upcoming NATO summit as potentially the most important in its history.
