Democrats think the best way to oust U.S. Rep. Brian Mast, R-Palm City, is focusing on his vote to repeal the Affordable Care Act, commonly called Obamacare.

On the campaign trail, liberal-leaning groups outside Florida's 18th congressional district have focused almost solely on his vote to repeal the law. His opponent, Democrat Lauren Baer, has made it the central focus of her campaign.

But Treasure Coast voters have a mixed opinion on ACA, with 51 percent supporting the law and 37 percent opposing it, according to a Public Policy Polling poll commissioned by Texas-based health care advocacy coalition Protect Our Care.

More than 74,000 district residents could have lost their health insurance under the American Health Care Act, according to a study by liberal-leaning think tank Center for American Progress.

In a race that Democrats believe is steadily tilting more in Baer's favor, progressive groups are expected to keep doubling down on Mast's stance on health care.

Obamacare repeal

Treasure Coast residents are conflicted about Republicans' attempt to repeal ACA last year, with 48 percent opposing it and 46 percent supporting it, according to the poll.

The poll found 49 percent of respondents would vote for a congressional candidate who is “a Democrat who supports the Affordable Care Act and wants to improve it.” That compares to 44 percent who would vote for “a Republican who wants to repeal” it.

Mast supported the repeal, calling it a "good bill" in an interview with TCPalm in May 2017, when the bill was making its way through Congress. He still thinks so, citing more funding for the state's Medicaid program and more private options for health coverage.

"The goal was to create more choice, more options for individuals, and that's why I voted for it," Mast said. "I think it's going to achieve those things."

More: Mast gets blasted on health care at Stuart town hall

Mast received significant backlash for that vote during a series of town hall meetings throughout the district, where voters bashed the first-term congressman and told him their stories of how ACA improved their lives.

Baer has said she decided to run after Mast voted in favor of the repeal.

She said she urged Mast not to vote for the bill, explaining to his staff how her mother, Nancy Baer, had chronic health issues from a car accident over two decades ago.

Since launching her campaign, she's held several meetings with potential voters about health care policy, and brought high-profile Democrats for local ACA-focused visits.

More: House Minority Whip Steny Hoyer discuss health care in Fort Pierce

Her campaign also has run multiple television ads about the bill.

Baer acknowledged the bill isn't perfect, but said she'd rather improve on it rather than repealed it, which a majority of voters polled support.

Mast accused Democrats of exaggerating the effects of the bill and cherry-picking facts to make Republicans, including himself, look callous.

He especially criticized Democrats for citing a Congressional Budget Office statistic that says 23 million people would not have health insurance by 2026 if ACA was repealed. Mast said most of those are people who would choose to not carry health insurance if the "individual mandate" clause in ACA didn't require it.

"I believe you should have the right to choose whether to purchase a product or not, especially if it's on the individual market," Mast said.

The budget office said there would be other reasons people would forego insurance, including higher premiums and fewer low-income and disabled people qualifying for Medicaid.

Baer disagrees. She worries repealing the mandate will cause the health insurance markets to destabilize, causing a rise in premiums, more people going to emergency rooms for medical treatment and costs shifting toward taxpayers.

More: Who pays when someone without insurance shows up in the ER?

She also said people don't "choose" not to have health insurance. They forego it only because they can't afford it.

Medicare for all

Neither candidate supports Medicare for All, a policy backed by progressives including Bernie Sanders, a Vermont senator and 2016 presidential candidate, and Andrew Gillum, the Tallahassee mayor who's running for Florida governor.

Baer said the plan would "explode" the national debt.

She favors a policy backed by Sen. Chris Murphy, D-Connecticut, and other moderates called "universal access to medical care," which would allow people and corporations to buy into Medicare and Medicaid. If they could not afford to purchase health care, government subsidies would be provided to offset health care costs.

District 18

District 18 covers Martin, St. Lucie and northern Palm Beach counties.

Nonpartisan political analysts — Cook Political Report, Sabato's Crystal Ball and Inside Elections — predict Mast will win, but faces a tough battle. But Baer hopes to ride into the seat on an anti-Trump, pro-woman, pro-Democrat Blue Wave.

The same Public Policy Polling poll that asked voters about ACA shows Mast leads Baer by three points, with a 4.2 percent margin of error and 10 percent of respondents still undecided. Among likely voters, 46 percent preferred Mast, while 43 percent preferred Baer, according to the poll of 533 district residents from Sept. 17-18.

Internal polling Baer's campaign released this week says Baer is closing the gap, with Mast leading her by three points instead of the previous six. Internal polls often favor the candidate releasing them.

Mast's campaign said its own internal polling doesn't match those results, but declined to release its findings to TCPalm.

Mobilizing support

Floridians for a Fair Shake hammered Mast for his vote to repeal ACA earlier this year.

The dark-money group based outside the district aired television ads and launched a massive social media campaign attacking Mast on his health care record.

Mast's campaign has brushed off the group's criticism and pointed out such PACs don't have to disclose who's funding their advertisements.

The group hasn't attacked Mast in several months, instead focusing its attention on ousting Rep. Vern Buchanan, R-Longboat Key.