 This is Nuala McGovern with NewsHour from the BBC World Service. The NATO summit, as we've been mentioning, has been held at the moment in Washington, D.C. Its leader is Joe Biden, who is hosting it. But he's also the person who's coming under increasing pressure to drop out of the US presidential race. Several Democratic members of Congress have added their voice to the chorus. The leader of Mr. Biden's party in the US House of Representatives, Hakeem Jeffries, has said he will relay the concerns to the White House.