Transcript for Joe Biden campaigns in key primary state
up, democratic presidential candidates out in force this weekend, targeting key primary states and taking aim at president trump. ABC's white house correspondent Tara Palmeri is on the lawn of -- north lawn with the story. Reporter: The democratic debate is next month in June. More candidates than spots. While they may be aiming their fire at president trump, the real competition is among themselves and many of these candidates have been crisscrossing the country to gain the support to qualify for these debates. I remember when people said that Barack Obama couldn't be elected. Reporter: As the democratic field grows wider by the day, with more than 20 candidates, front-runner Joe Biden in the battleground state of south Carolina this weekend, swinging hard at president trump. Above all else we must defeat Donald Trump. Reporter: While president trump claims this is his campaign message -- I'll be running on the economy. Reporter: White house chief of staff Mulvaney saying that president trump doesn't see Joe Biden as the favorite. Four declared candidates descending on the battleground of Texas. Mayor Pete buttigieg's speech in Dallas without controversy. The openly gay candidate heckled by protesters. Former Texas congressman Beto O'rourke defending his opponent in his home state. The hatred directed towards Pete buttigieg last night was not reflective or representative of my state. Reporter: Later, making a bold statement, president trump must faces consequences from the results of the Mueller report. No man regardless of his position is above the law. Reporter: Another top topic on the campaign trail was attorney general William Barr's handling of the Mueller report. A lot of these candidates are calling on him to resign, like senator kamala Harris and senator Cory booker. But there was one leading candidate who didn't go that far and that was senator Bernie Sanders. Tara, thank you. Speaking of Bernie Sanders, this morning, the senator from Vermont is reacting to the new candidacy, relatively new candidacy of the apparent front-runner Joe Biden. ABC's chief white house correspondent Jon Karl hit the trail with Bernie Sanders. Take a listen. I'm sure you heard that Joe Biden said he's the most Progressive candidate in this race. Joe is a good friend of mine. I'm not here to attack Joe. Joe voted for the war in Iraq. I led the effort against it. Joe voted for nafta and trade agreements with China. I led efforts against that. Joe voted for deregulation of Wall Street, I voted against that. I think if you look at Joe's record and you look at my record, I don't think there's much question about who's more Progressive. Jon, good morning. I love when people say, he's my friend and I'm not going to attack him, and then they go on and attack him. Do these comments we just heard from the senator indicate that Joe Biden has a serious problem on his left flank here? Reporter: Well, Dan, what they indicate is that we're going the see in this primary a battle for the ideological soul of the democratic party. These are significant real differences. Bernie Sanders is not waiting to take aim at Joe Biden and, by the way, Elizabeth Warren is also showing that she's willing to take on Biden. This primary is going to be very interesting and, you know, usually you have a period where the candidates wait before taking on one another but that is not happening here. The battle is on. Yeah, everyone has to make their mark in such a crowded field. Let me switch subjects now politically speaking, talk about international affairs. We have new video of north Korean leader Kim Jong-un personally overseeing some missile launches this weekend. You have secretary of state Mike Pompeo on the show this morning. What does this mean for president trump who has staked his reputation at least in part on his peace negotiations with this unpredictable dictator? Reporter: Well, I think you point to the key factor here, you see Kim Jong-un personally overseeing these military tests. Look, this was not a nuclear test. It was not an intercontinental ballistic test. Those are the two that north Korea has promised to not do while these negotiations go on. But this was clearly a provocation and a provocation overseen by the man that the president trump calls his friend and says that he's confident he can work out with. He comes as North Korea says they're essentially putting a deadline, they want to see action, they want to see something from the United States before the end of the year. I think we are nearing a very critical inflection point with the North Korea talks and it will be very interesting how Mike Pompeo responds to all this. He has been much more skeptical about North Korea's intentions than his boss, the president. Jon, thank you very much. Always great to talk with you on a Sunday morning. I want to remind everyone -- Jon has a big show this morning. More from that exclusive interview on the campaign trail with senator Bernie Sanders. Plus, as discussed, he'll go one-on-one with secretary of state Mike Pompeo. For the latest on the u.s.'s response to both North Korea and the ongoing crisis in Venezuela. It's all coming up on "This week" later this morning right here on ABC.
This transcript has been automatically generated and may not be 100% accurate.