https://www.theguardian.com/world/2018/feb/19/china-and-us-in-skirmish-over-nuclear-football-during-trump-visit-to-beijing-report

Chinese officials had blocked the entry of the US military aide carrying the “nuclear football”, a black leather satchel containing the codes that allow the president to launch a nuclear strike.

A US official reportedly then rushed into an adjoining room to inform US chief of staff John Kelly of what was happening. “Kelly rushed over and told the US officials to keep walking – ‘We’re moving in,’ he said – and the Americans all started moving.

The ‘nuclear football’ - the deadly briefcase that never leaves the president’s side
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“Then there was a commotion,” Axios reported. “A Chinese security official grabbed Kelly, and Kelly shoved the man’s hand off of his body. Then a US secret service agent grabbed the Chinese security official and tackled him to the ground.”