And so will President Obama, making the case that his former secretary of state is the nation's best hope of coming together and staying safe.

　　Correspondent John Yang begins our coverage:

　　JOHN YANG: At the White House, President Obama prepared for his last convention as president.

　　QUESTION: How do you feel about tonight, Mr. President?

　　BARACK OBAMA, President of the United States: What's happening tonight? Oh. That was a joke. You look so serious.

　　I feel great.

　　JOHN YANG: Also on the program tonight, Vice President Biden, and Hillary Clinton's choice to be the next vice president.

　　This morning, Virginia Senator Tim Kaine spoke to home state delegates.

　　SEN. TIM KAINE (D-VA), Vice Presidential Nominee: She's going to open up who we are as a nation, who the leadership of this nation is. And people are going to be able to see themselves in that office who never could have imagined it before. I think it's great for men to be able to stand and support strong women leaders all across this nation.

　　JOHN YANG: Away from the convention, more fireworks over those hacked Democratic National Committee e-mails. American intelligence officials say it appears to be the work of the Russian government.

　　Today, Donald Trump added fuel to the fire.

　　奥巴马总统表态支持希拉里

　　DONALD TRUMP (R), Presidential Nominee: I will tell you this. Russia, if you're listening, I hope you're able to find the 30,000 e-mails that are missing. I think you will probably be rewarded mightily by our press. Let's see if that happens.

　　JOHN YANG: The Clinton campaign said that moved it from being a political issue to a question of national security.

　　Back in Philadelphia, Bernie Sanders urged supporters to close ranks behind the woman who defeated him.

　　SEN. BERNIE SANDERS (I-VT): It is not good enough just to elect Hillary Clinton. It is to transform America, and to make sure that we have a Democratic Senate, a Democratic House and a Democratic president who will do that.

　　JOHN YANG: Last night, dozens of Sanders delegates walked out of the convention.

　　WOMAN: We don't believe that Clinton is a true Democrat. We don't think she really believes in a true democracy. You count every vote, in every state, and you make sure they all have every right to vote, in every single way. She doesn't care about that. She has taken away our votes and our voice. We're making sure we're heard.

　　JOHN YANG: In an interview with NBC's "Today Show," Mr. Obama called for unity.

　　BARACK OBAMA: One of the dangers in an election like this is that people don't take the challenge seriously, they stay home, and we end up getting the unexpected.

　　JOHN YANG: A message he will bring directly to the delegates tonight.

　　For the "PBS NewsHour," I'm John Yang in Philadelphia.

　　GWEN IFILL: Next, we head down to the convention floor, where NPR's "Weekend Edition Sunday" host, Rachel Martin, is standing by. Rachel joins us every night this week as part of our joint "PBS NewsHour" and NPR convention coverage.

　　Rachel, what do we expect tonight?

　　RACHEL MARTIN: Hey, Gwen.

　　So the last couple of nights here at the Democratic National Convention have been about healing those wounds caused in the primary battle. Tonight, Democrats are going to try to turn the page. The focus is going to be on two very important issues, national security and the economy.

　　Over the past couple of days, Donald Trump has really hammered the Democrats, saying, where's the conversation about ISIS? Where's all the talk about the threat from terrorism? Tonight will be the Democrats' chance to answer that and they will do it with some heavy hitters, one of them, Leon Panetta, a former director of the CIA and former director of defense.

　　He will take the stage and make the case as to why Hillary Clinton should be the next commander in chief. Also, on the economy, another heavy hitter, Vice President Joe Biden, he has said that Democrats have kind of forgotten how to talk to white working-class voters. He's going to reach directly out to those voters with his message tonight.

　　We will also hear from Tim Kaine, Hillary Clinton's vice presidential pick. And, finally, closing out the evening, the keynote address will be from Barack Obama, arguably Hillary Clinton's most powerful surrogate. All eyes will be on him and his message this evening — back to you.

　　JUDY WOODRUFF: Thank you, Rachel. We will be talking to you throughout the night.