The 2024 presidential race is entering a critical stretch, with Vice President Kamala Harris and former President Donald Trump set to debate and the first swing state ballots hitting mailboxes shortly after the Labor Day holiday weekend.

As the calendar turns to September, both campaigns are focusing on on key battleground states — with Harris eyeing an expanded map and Trump digging in across the Upper Midwestern states that delivered him the presidency in 2016 and ousted him from office in 2020.

Meanwhile, voting will begin this week. The first ballots of the 2024 election will go out Friday in North Carolina, one of a handful of potentially critical Sun Belt states. Then, two weeks later, early in-person voting starts in Minnesota, South Dakota and Virginia.

Harris last week focused on the Sun Belt, with a bus tour in Georgia and her running mate, Minnesota Gov. Tim Walz, also visiting North Carolina.

“I think we know: Very difficult for a Republican presidential candidate to win the White House if they can’t win North Carolina,” Walz said Thursday during a stop at a campaign field office in Raleigh.

Harris’ campaign is pouring money into advertising in the Savannah media market as it seeks to broaden its appeal outside Atlanta. According to AdImpact data, Harris’ campaign has spent a total of about $1.7 million in advertising there over the last three weeks.

Harris’ top campaign adviser said in a memo Sunday the vice president remains the “clear underdog” in the race, setting expectations and looking to guard against complacency as the fall campaign season begins.

Jen O’Malley Dillon, the Harris campaign chair, wrote that Trump retains a “motivated base of support,” and predicted a close contest.

Pointing to the September 10 debate and an increased pace of travel, O’Malley Dillon said the weeks ahead will be critical in defining the Democratic ticket.

Trump, meanwhile, has turned his attention to the “blue wall” of Pennsylvania, Michigan and Wisconsin, holding events in all three states late in the week and promising an economic revival.

“I’m here today with a simple message for the American autoworker and for the American worker: Your long economic nightmare will very soon be over,” the former president said at the start of his remarks at a steel distribution company in Potterville, Michigan.

The candidates are interspersing their campaigning with preparation for their September 10 debate, hosted by ABC. That debate — the first between Harris and Trump, and the only one both campaigns have agreed to so far — could prove the most pivotal moment in the 2024 race.

Trump has enlisted the help of former Hawaii Democratic Rep. Tulsi Gabbard, whose failed 2020 presidential bid featured several notable clashes on debate stages with Harris over foreign policy and Harris’ record on criminal justice. Harris, meanwhile, is working closely with Philippe Reines, a longtime aide to Hillary Clinton, who is reprising his role playing Trump at the request of the Harris campaign.

Polls show a tight race nationwide and in critical swing states. A Wall Street Journal survey released Thursday found no clear leader, with Harris at 48% to Trump’s 47% among registered voters. A Quinnipiac University poll out the same day similarly found Harris at 49% and Trump at 47% among likely voters.

Sun Belt states that once appeared to have slipped out of Democratic reach have reemerged on the battleground map since Harris became the party’s nominee. Fox News polls released Wednesday found no clear leader among registered voters in Arizona, Georgia, Nevada and South Carolina. The polls found Harris at 50% to Trump’s 49% in Arizona; those numbers flipped, with Trump at 50% and Harris at 49%, in North Carolina. In both Georgia and Nevada, Harris was at 50% to Trump’s 48%.

An election that isn’t all about Trump

More than a month after the Democratic change at the top of the ticket, with President Joe Biden dropping his reelection bid and Harris stepping in, Democrats believe they still have momentum.

Hawaii Sen. Brian Schatz said in an interview that the race has shifted from one where Democrats were on track to lose and in need of a fundamental shake-up, to one where Republicans are “hoping that there’s some catastrophic moment” in which Harris blows it.

“They’re clearly taken aback by a change in the candidate. But it’s the candidacy that I think is throwing them off. They’ve never run with against someone with such an orientation towards the future,” Schatz said.

“It was always about how you felt about Donald Trump – you were either for Donald Trump or not for Donald Trump or ambivalent. And I think what’s happening is after more than eight years a lot of people would just like not to talk about that man anymore,” he said. “Lots of politicians have attempted to be the leader that could help us to turn the page as a nation and Kamala Harris is evidently the only one that is capable of doing that.”

Republicans, meanwhile, are arguing that Harris’ economic proposals, and her promises of a new era in American politics, are hollow, since she has been vice president for three and a half years and bears at least partial ownership of Biden’s record.

“If she wants to tackle the affordability crisis or close down the southern border, she should be doing it now,” Republican vice presidential nominee Sen. JD Vance said Friday on “CNN News Central.” “And I think it takes a lot of shame — shamelessness, I should say — to be able to stare at the American people’s eyes and say, I’m going to fix your problems now, when I’ve already been in power for three and a half years.”

Battle for women’s votes

Polls have shown Trump with an advantage among men who are likely to vote, but Harris with a huge edge with women. That split is common in presidential elections, but Trump is attempting to chip away at Harris’ advantage with women in part through a focus on reproductive rights.

It’s a topic that has been a huge Democratic advantage since the Supreme Court, with a conservative majority that includes three members appointed by Trump, in 2022 overturned Roe v. Wade’s nationwide abortion rights protections — opening the door to a new patchwork of state-level restrictions.

Trump last week infuriated conservatives with his answer to a question about how he plans to vote on a referendum that will decide the future of abortion access in his home state of Florida.

Under current Florida law, abortion is illegal in most cases after six weeks. Voters this fall will decide on a ballot measure that would make abortion legal in the state up to the point of viability, which many experts believe is around 23 or 24 weeks of a pregnancy.

Trump had repeatedly declined to weigh in on the referendum, but on Thursday, he told NBC that Florida’s six-week ban was “too short” and said he would be “voting that we need more than six weeks.”

A day later, he said he was going to vote “no” on the referendum and, in explaining why he was doing so, repeated a false claim that Democratic states are passing laws that allow people to execute babies after birth.

Also on Thursday, while campaigning in Michigan and Wisconsin, he offered a new proposal aimed at women, pledging universal coverage of in vitro fertilization.

“Under the Trump administration, your government will pay for – or your insurance company will be mandated to pay for – all costs associated with IVF treatment,” Trump said during a campaign event in Michigan. “Because we want more babies, to put it nicely.”

However, senators in his own party, including his running mate, Vance, defeated a bill with a similar provision earlier this summer.

On a Harris campaign call with reporters on Friday, Massachusetts Sen. Elizabeth Warren said Trump’s promise to have fertility treatments paid for is “just smoke and mirrors” without a commitment to protect the treatments from legal threats.

She pointed to the Alabama Supreme Court ruling earlier this year that deemed that frozen embryos are children, jeopardizing the legality of IVF treatments before Alabama’s Republican governor signed a law protecting IVF access in the state after Trump said he supports the treatment.

She also cited a Senate bill to codify access to IVF nationwide that was blocked by Republicans in June and a House GOP bill that seeks to legally define life as beginning at the moment of conception or fertilization to draw the contrast on protections for reproductive health care.

“Making vague promises about insurance coverage does not stop a single extremist judge or state legislature from banning IVF. Making vague promises about insurance coverage does not stop a single one of the 131 Republicans in Congress from advancing their fetal personhood bill that would ban IVF. Despite what Trump seems to think, American women are smart and we aren’t falling for his gaslighting,” Warren said.

Harris’ campaign on Friday also countered Trump by announcing a new bus tour aimed at advocating for women’s reproductive rights. The “Fighting for Reproductive Freedom” bus tour will kick off Tuesday in Palm Beach, Florida – Trump’s hometown – with Minnesota Sen. Amy Klobuchar, Harris-Walz campaign manager Julie Chavez Rodriguez, CNN senior political commentator Ana Navarro and reproductive rights storyteller Anya Cook.

Missing specifics on policy

It wasn’t just Trump’s pledge of universal coverage of IVF that lacked details.

Both Harris and Trump have discussed policy through the lens of details and aspirations, rather than addressing the difficult questions about the exact contours of their proposals, how they’d win approval on Capitol Hill and how they’d be funded — all of which would confront them in the Oval Office.

Harris has said she would aim to help the middle class by targeting price-gouging, making housing more affordable through $25,000 in down-payment support for first-time homebuyers, offering a child tax credit, lowering drug prices and creating new jobs.

Trump, meanwhile, has pledged the largest deportation effort in US history, and has said it would involve the National Guard and perhaps the military. But he has not addressed how he would solve the constitutional, logistical and manpower issues that such an undertaking would involve.

He has also ducked specific questions about abortion rights, claiming he could bring about a national consensus policy on an issue that has been a wedge in American politics for more than 50 years.

In fact, the most detailed policy blueprint in the 2024 race — “Project 2025,” a 920-page document organized by The Heritage Foundation think tank and developed in significant part by people who served in Trump’s administration — is one Harris’ campaign has used to attack Trump, while the former president distanced himself from it.

The missing details could be fleshed out when Harris and Trump meet for their first debate on September 10. Another key moment will come on October 1, when CBS hosts the vice presidential debate between Harris’ running mate, Walz, and Trump’s No. 2, Vance.

This story has been updated with new reporting.

CNN’s Daniel Strauss, Steve Contorno, Aaron Pellish, Ali Main, Ebony Davis, Priscilla Alvarez, Kit Maher and Kevin Liptak contributed to this report.