(NewsNation) — In the first debate between the vice presidential candidates, Sen. JD Vance defended former President Donald Trump‘s health care record, claiming Trump had improved the Affordable Care Act during his term.

“Donald Trump could have destroyed the program. Instead, he worked in a bipartisan way to ensure that Americans had access to affordable care,” Vance said.

Democratic Gov. Tim Walz sharply disagreed, accusing Trump of attempting to dismantle the ACA.

“Donald Trump, all of a sudden, wants to go back and remember this: he ran on the first thing he was going to do on day one was to repeal Obamacare,” Walz said.

Both candidates agreed on the need for a functioning Health Insurance Marketplace but differed on how to achieve it.

Vance argued that Trump’s leadership led to more people obtaining private insurance, reduced prescription drug costs, and introduced price transparency

Health care costs remain a significant issue for many Americans, with both parties vying to convince voters of their plans to address affordability and access. And ObamaCare and its pre-existing conditions protections have been a political third rail in recent years.

A record 21.3 million people have signed up for health care insurance through the HealthCare.gov Marketplace for 2024, making a third consecutive banner year for the program.

The marketplace, created under the Affordable Care Act — also known as Obamacare — added 5 million more people than in 2023.

Walz praised Vice President Kamala Harris for expanding health care coverage and negotiating Medicare drug prices.

“The way she made everything better was negotiating those 10 drugs on Medicare for the first time in American history,” Walz said.

The debate moderator pressed Vance to explain how Republicans would protect people with pre-existing conditions, a key provision of the ACA.

Vance insisted that current laws protecting those with pre-existing conditions would remain, adding, “We want to keep those regulations in place, but we also want to make the Health Insurance Marketplace function a little bit better.”

On the presidential debate stage, Trump said he had “concepts of a plan” to replace the health law if it were repealed, drawing ridicule from Democrats. Trump’s official platform doesn’t mention Obamacare at all. 

Walz warned that Republican plans could allow insurers to discriminate against older and sicker individuals. “What they’re going to do is let insurance companies pick who they insure,” he said.

What to know about the politics behind Obamacare

The Affordable Care Act, or ObamaCare, has experienced a significant political renaissance. 

Almost as soon as the law was passed in 2010, it became an albatross for Democrats. It cost them control of the House and Senate, and Trump pledged to “repeal and replace” the health law on his way to winning the presidency in 2016.

But after Trump and congressional Republicans failed to repeal the law in 2017 by a single vote, its popularity soared. Democrats won back control of the House in the 2018 midterms in part by campaigning on protecting preexisting conditions.    

When Trump was elected in November 2016, just 43 percent of adults supported Obamacare, according to a tracking poll conducted by the nonpartisan health research group KFF. The most recent poll published in May showed 62 percent of respondents view the law favorably.

For instance, the fiscal 2025 budget proposal from the Republican Study Committee, which includes most of the House GOP caucus, recommends removing many of the existing protections for people with preexisting conditions, including allowing states to offer separate risk pools for younger, healthier people.  

Experts have said high-risk pools can work in theory if they are sufficiently subsidized by the government. For more than 35 years, before the ACA passed, red and blue states alike used high-risk pools to cover people with expensive medical conditions separately from the rest of the insurance market.   

However, the pools lacked sufficient funding and so rarely succeeded in covering people who needed insurance the most.

Polls show voters want to hear about plans to lower health costs. And according to a KFF tracking poll released earlier this month, voters trust Harris to do a better job than Trump on health costs by a 48-to-39-percent margin. 

NewsNation partner The Hill’s Nathaniel Weixel contributed to this report.