Prosecution, defense offer competing causes of George Floyd's death.
Prosecutor: Ex-officer Derek Chauvin "betrayed" his badge, used excessive and unreasonable force on George Floyd.
Dispatcher: Called sergeant while watching video of Floyd arrest; felt "something wasn't right," was "voicing my concerns".
Biden warns war against COVID-19 "far from won".
First real-world study finds Pfizer, Moderna vaccines 90% effective after two doses, 80% effective after one.
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The Situation Room with Wolf Blitzer and Pamela Brown