US President Donald Trump arrives to board Air Force One at Joint Base Andrews in Maryland on April 26, 2019.

It's not surprising that health care has become a top priority for voters, because the last few years have been "tumultuous" for the health-care system, said Rachel Nuzum, vice president for the Federal and State Health Policy initiative at The Commonwealth Fund.

While 23% of those polled said Trump's stance on health care would compel them to vote for his reelection, 40% said they likely will not support him next year because of it. Of the remaining voters, 33% said health care is not a factor in who they'll vote for, while 5% said they had no opinion on Trump's handling of health care.

More Americans say they are likely to oppose rather than support President Donald Trump in the 2020 presidential elections because of his handling of health care, according to a new ABC/Washington Post poll .

"Americans need certainty when it comes to their health care," Nuzum said. And Trump's call to upend the health-care system "creates a lot of uncertainty," she added.

Trump and congressional Republicans have vowed to repeal the Affordable Care Act, or Obamacare, pledging to deliver on one of Trump's main campaign promises. Despite Trump's assertion that Republicans will become "The Party of Healthcare," Republicans don't have another health-care plan in place and are waiting until the GOP regains control of the House of Representatives to unveil a replacement proposal. Republicans currently hold control of the Senate but lost the majority of the House in the 2018 midterm elections.

Lawmakers on both sides of the aisle widely believe the Republican-led Senate's attempt to repeal Obamacare in 2017 led to the Democrats' House victory.

Trump's effort to repeal Obamacare without a better proposal in place is a "very risky political proposition," according to John Hudak, a senior fellow and deputy director at the Brookings Institution's Center for Effective Public Management.

Hudak said Obamacare's individual provisions — such as Medicaid expansion, protecting preexisting conditions and allowing children to stay on their parents' insurance plans until they are 26 years old — are "wildly popular" with voters.

"These are all issues that are not just more popular than the president, they're more popular than a lot of other issues in America," Hudak said.

But Obamacare is in jeopardy once again, after the Trump administration supported a lawsuit questioning the health-care law's constitutionality.

In December, U.S. District Judge Reed O'Connor of Texas said that without a rule that requires Americans to have health insurance or face a tax penalty, Obamacare cannot stand. The Trump administration reduced the tax penalty — called the individual mandate — to $0 in the 2017 Tax Cuts and Jobs Act.

Now O'Connor's ruling, which is backed by the Justice Department, awaits deliberation in the U.S. Court of Appeals for the 5th Circuit, though experts and even some top Republicans have said it's unlikely the law will be overturned.

Though some believe Obamacare is safe from a negative ruling from the Supreme Court, Hudak said Trump's attacks on Obamacare, which has become popular with many citizens despite failing to reduce health-care costs, can hurt his relationship with swing voters.

"Threatening to take away tens of millions of people's health care is not a great recipe for growing his political coalition," Hudak said.