Arizona Sen. Mark Kelly, who is seen as a strong Democratic vice presidential pick, defended the vice president's record on immigration and went on the attack against Republican vice presidential candidate JD Vance, in an interview on "Morning Joe" on Wednesday.

"Donald Trump and Senate Republicans, what did they do several months ago? We had a bipartisan bill that we negotiated faithfully with the administration, both sides of the aisle, and Donald Trump said that Senate Republicans can't vote for it," Kelly said. "He wanted to talk about this issue instead of actually fix it and JD Vance and other Republicans, they ran away from it."

He said Vance, who plans to visit the U.S.-Mexico border Wednesday, should instead be back in Washington passing legislation on the border.

"I mean, JD Vance is down here," Kelly said. "I think he's in Arizona today probably getting a photo op at the southern border. Kamala Harris is about solving problems. Donald Trump wants to take us, drag us back a decade."

Kelly said, in contrast, Harris wants to address border and immigration.

"She's worked on this problem for three-and-a-half years and it's a challenging problem. I mean, I represent a border state. But we have made progress, especially with what was put in place over the last several months," Kelly said defending Harris. "But I can't stress more that this is an issue that Donald Trump and Republicans just want to talk about."

When asked what he thought Harris needed in a running mate, Kelly said, "That's going to be something that the vice president is going to have to figure out."

"I think she's got a lot of great choices out there," he added. "My focus is not on this, and this is not about me. I mean, this is about the future of our country."

-ABC News' Fritz Farrow

Next week, Vice President Kamala Harris and her future running mate will crisscross the country together, a source familiar confirmed to ABC News.

Beginning Tuesday, the vice president and her running mate will hit all seven battleground states starting in Pennsylvania.

The source said to read too much into the fact that Philadelphia is first up, even though Pennsylvania Gov. Josh Shapiro has been out stumping for Harris and auditioning publicly for the role.

Harris and her running mate will then head to Wisconsin, Michigan, North Carolina, Georgia, Arizona and end in Nevada.

ABC News' Mary Bruce

Vice President Kamala Harris was the only candidate to qualify for the Democratic party's presidential nominating ballot, the Democratic National Committee (DNC) announced Tuesday night.

The virtual roll call to make Harris the official Democratic nominee will begin Thursday, Aug. 1, and will end on Monday, Aug. 5.

Across the country, 3,923 delegates petitioned to make Harris the Democratic nominee, according to the DNC, which noted Harris secured the support of 99% of participating delegates.

Republican Vice Presidential candidate JD Vance said it was "time to circle the wagons and load the muskets," in a forward to a book penned by Project 2025's leader, according to a report.

The New Republic obtained the forward to "Dawn's Early Light," the book written by the Heritage Foundation leader Kevin Roberts, where Vance claims "explores many of the themes I’ve focused on in my own work."

"Never before has a figure with Roberts’s depth and stature within the American Right tried to articulate a genuinely new future for conservatism. The Heritage Foundation isn’t some random outpost on Capitol Hill; it is and has been the most influential engine of ideas for Republicans from Ronald Reagan to Donald Trump," Vance wrote in the forward, according to the report published Tuesday.

Vance claims "Roberts sees a conservatism that is focused on the family," and "cultural norms and attitudes matter."

The senator ended his forward with an analogy about a garden that "needs to be recultivated."

"As Kevin Roberts writes, 'It’s fine to take a laissez-faire approach when you are in the safety of the sunshine. But when the twilight descends and you hear the wolves, you’ve got to circle the wagons and load the muskets,'" Vance wrote, according to the report. "We are now all realizing that it’s time to circle the wagons and load the muskets. In the fights that lay ahead, these ideas are an essential weapon."

-ABC News' Soo Rin Kim