Savannah, Georgia - Kamala Harris defended her policy shifts on key issues Thursday, insisting in the first interview of her presidential campaign that her "values have not changed."

The 59-year-old Democrat also said that she would name a Republican to her cabinet if she wins November's election in her joint CNN sit-down with her running mate Tim Walz.

Rival Donald Trump branded the US vice president the "greatest flip-flopper" as he addressed a rally in the swing state of Michigan.

Harris said her positions had evolved on the issues of fracking, which she previously opposed, and migration over the Mexican border, on which she has taken an increasingly tough stance.

"I think the most important and most significant aspect of my policy perspective and decisions is my values have not changed," Harris said in an excerpt of the CNN interview. The full version is being screened at 9 PM local time.

Republicans had criticized Harris for not giving any interviews since President Joe Biden dropped out of the White House race nearly six weeks ago.

Harris has enjoyed a honeymoon period with surging polls and record fundraising but has also faced scrutiny for keeping many of her policies vague.

But in a gesture of unity, she said it would be to the "benefit of the American public" to have a Republican in her cabinet if elected.

The first female, Black, and South Asian vice president in US history meanwhile brushed aside Trump's recent comments questioning her racial identity. "Same old, tired playbook," she said.

Harris gave the interview while on a campaign bus tour of Georgia, one of the seven battleground states that are expected to decide the November 5 election.

A number of polls out Thursday showed Harris ahead of Trump, if only marginally, with several of them finding increased support for Harris in battleground states.

A Bloomberg/Morning Consult poll found Harris leading in six out of the seven swing states, while a Fox poll also showed increasing support in the battlegrounds.

At a rally in Savannah at the end of the two-day swing in Georgia, which Democrats flipped from Trump in 2020, she admitted it was "going to be a tight race until the very end."

Trump has himself been hitting the campaign trail hard in recent days, after a period where the 78-year-old former president appeared to struggle to find his footing against a new, younger, female candidate.

Speaking at an event in Potterville, Michigan, on Thursday, Trump targeted Harris on her immigration policy shifts: "Now she's saying, 'Oh, we want to build a strong border."

"Where has she been for three and a half years?"

Yet both Trump and Harris appear to be making gestures towards the center ground.

Trump said in an interview with NBC News Thursday that if elected, either the government or insurance companies would cover the cost of in vitro fertilization (IVF) for Americans.

Reproductive rights have been a major vulnerability for Trump since the Supreme Court gutted federal protections for abortion access in 2022, and an Alabama court ruled in February that frozen embryos created via IVF should be considered children.

Harris's speech meanwhile focused on the cost of living. She repeated her pledge to give tax cuts to families in the first year of a child's life "to help pay for that car seat, or the crib, or the baby clothes."

Her CNN interview is being closely watched in a year where big set-piece political events have shown their ability to produce surprises, like Biden's debate disaster on June 27 that led to him quitting the race.

Harris and Trump are set to face off in their pivotal first debate on September 10 in Philadelphia.