AMNA NAWAZ: Welcome to the "News Hour."

With both party conventions in the rearview mirror, the 2024 presidential campaign enters its final stage.

There are now new questions about if the candidates will debate at all.

And, today, Donald Trump turned his attention to national security and Kamala Harris' record.

Lisa Desjardins has this report.

(APPLAUSE) DONALD TRUMP, Former President of the United States (R) and Current U.S. Presidential Candidate: Well, thank you.

LISA DESJARDINS: Former President Donald Trump campaigning in battleground, Michigan, addressing an annual meeting of the National Guard Association, as he seeks a second term as commander in chief.

DONALD TRUMP: And it's why I'm here today, because America's future is under threat like never before, right at this moment.

LISA DESJARDINS: Trump accused the Biden/Harris administration of disastrously mishandling the Afghanistan withdrawal.

The Biden administration has said its decisions were set in motion by Trump's agreement to pull out American troops.

In the chaos exactly three years ago today, a suicide bomb attack in Kabul left 13 American service members killed.

DONALD TRUMP: Kamala Harris, Joe Biden, the humiliation in Afghanistan set off the collapse of American credibility and respect all around the world.

LISA DESJARDINS: This morning, Trump laid wreaths at Arlington National Cemetery in their memory.

Meanwhile, Vice President Kamala Harris and running mate Minnesota Governor Tim Walz were off the campaign trail today, but they are awash in cash, reporting a haul of more than a half-billion dollars since launching a month ago, including $82 million during last week's convention alone.

In the meantime... KRISTEN WELKER, Moderator, "Meet The Press": Welcome back to "Meet the Press."

SEN. J.D.

VANCE (R-OH), Vice Presidential Candidate: Thank you.

Thanks for having me.

LISA DESJARDINS: ... the man who wants Harris' current job faced direct questions on NBC's "Meet the Press" over the weekend.

KRISTEN WELKER: Can you commit, Senator, sitting right here with me today, that if you and Donald Trump are elected, that you will not impose a federal ban on abortion?

SEN. J.D.

VANCE: I can absolutely commit that, Kristen, and not only have to veto it.

KRISTEN WELKER: So, he would veto a federal abortion ban?

SEN. J.D.

VANCE: I think he would.

He said that explicitly that he would.

LISA DESJARDINS: Vance also was asked about his running mate, specifically Donald Trump's repeated words questioning if this election will be fair.

KRISTEN WELKER: Do you have faith the 2024 election will be free and fair?

SEN. J.D.

VANCE: I do, Kristen.

I do think it's going to be free and fair.

And we're going to do everything that we can to make sure that happens.

We're going to pursue every pathway to make sure, again, legal ballots get counted.

LISA DESJARDINS: Trump is signaling he may bow out of the first head-to-head debate scheduled for September 10, writing about host network ABC: "Why would I do the debate against Kamala Harris on that network?"

The Harris campaign said in a statement that the issue is more specific, that it wants microphones to remain on during any debate, and that the Trump campaign staff has not agreed.

Regardless, Monday morning, Trump would not commit to taking part, as planned.

DONALD TRUMP: Let's do it with another network.

I want to do it.

LISA DESJARDINS: The two campaigns will both be on the road this week, the Harris/Walz campaign touring in Georgia and Trump focusing on Michigan and Wisconsin.

For the "PBS News Hour," I'm Lisa Desjardins.