Why is Kamala Harris bringing Tim Walz to her first major interview?

“She’s not smart enough to do a news conference,” Mr Trump told media earlier in August. “She won’t do interviews with friendly people because she can’t do better than Biden.”

Ms Harris’s apparent hesitation to sit down for questions has fuelled the Republican narrative that the Harris-Walz campaign lacks in substance.

“I think it’s incredibly weak, weak sauce, to show up with your running mate,” said Scott Jennings, a former special assistant to President George W Bush, on CNN this week, adding that Harris had a “troubling lack of confidence” in her own political ability.

The Democratic nominee has enjoyed a surge in momentum since entering the race. Now, after her whirlwind introduction to American voters, she needs to “reinforce” that energy, said Republican strategist and Trump critic Chip Felkel.

“She’s gotta get out there,” he said. “She’s got to show that she can think under pressure, because that’s part of what the president has to do.”

But supporters of Ms Harris insist that given the breakneck nature of her candidacy, she is taking things at a smart pace.

“I think the cadence has been right,” said Peter Giangreco, a Chicago-based Democratic strategist. “Win the nomination, pick your nominee, lay out your economic plan, do your convention and now do some sit-downs and amplify that.”

Mr Giangreco predicted Ms Harris and Mr Walz will focus on their economic plan, an agenda to lower the cost of living and provide economic security that she first announced at a rally in Raleigh, North Carolina two weeks ago.

With that particular message, the presence of Mr Walz during this week’s interview may prove useful. The Minnesota governor has earned praise for his economic record while in office, including hundreds of millions in tax credits to families, and universal free school lunches.

Mr Giangreco also pointed to another potential benefit of a joint interview: drawing a contrast between Mr Walz and his Republican counterpart Mr Vance.

Since Mr Vance joined Trump’s ticket in July, the Ohio senator has made repeated stumbles, forced to defend past comments, like his derision of “childless cat ladies”.