 most effective defensive alliance in the history of the world. The president has put the NATO alliance at the center of his foreign policy. And this was a week he has sought to elevate his leadership on the world stage. But for Biden, this has also become a week that's a big test for his campaign. After a rocky debate, performance raised questions about his political future. Over the coming days, he'll be trying to reassure anxious allies. Asma Khalid, NPR News, the White House.