Sens. Patty Murray (D-Wash.) and Lamar Alexander (R-Tenn.). (J. Scott Applewhite/AP)

Henry Waxman is chairman of Waxman Strategies, a public affairs and strategic communications firm. He served as a Democrat in the House of Representatives from 1975 to 2015.

Conor Lamb’s stunning victory in last month’s special election for Pennsylvania’s 18th Congressional District makes clear that health care is a winner for Democrats in 2018. More than half of all voters ranked it as a top issue, according to exit polls, and Lamb won the votes of 64 percent of those who named it their No. 1 priority.

Republicans’ attempt last year to repeal the Affordable Care Act and send 32 million Americans into the ranks of the uninsured remains an albatross. Voters in the 18th District, where Donald Trump won by 20 percent, disapproved of the ACA repeal by 53 percent to 39 percent.

Lamb campaigned as a fierce supporter of the ACA, Medicare and Medicaid — something every Democrat should do. We should remind voters again and again that Democrats are committed to universal coverage while Republicans try to take people’s health insurance away.

But what Democrats cannot do is turn this winning issue into a loser by imposing litmus tests — in particular, by demanding that all Democratic candidates support a single-payer bill, such as Medicare for all.

I say this as someone who co-sponsored single-payer legislation with Sen. Edward M. Kennedy (D-Mass.) when I served in Congress, but who also sought to seize any and every opportunity to bring our nation closer to the goal of universal coverage. That’s why I authored laws expanding Medicaid to cover more low-income children in the 1980s and 1990s, why I sponsored the 1997 Children’s Health Insurance Program, and why I led the fight to enact the ACA.

These bills passed, expanding coverage to tens of millions of Americans, while single-payer never mustered majority support in Congress. If Democrats recapture Congress this fall, we should take a similar approach: working in the realm of the possible and building on what works, rather than trying to blow it up.

One priority must be to fix the ACA’s problems — most of which are the result of deliberate sabotage by the Trump administration and the Republican Congress — while also strengthening and expanding the law.

For starters, we need to restore cost-sharing reduction payments and pass other key provisions in Sen. Lamar Alexander’s (R-Tenn.) and Sen. Patty Murray’s (D-Wash.) bipartisan market stabilization bill — urgently needed legislation that was left out of March’s federal spending bill.

We should expand subsidies so they don’t cut off for those earning more than 400 percent of the poverty level, by changing the formula so that no family’s health care premiums exceed 10 percent of their income. This would be a relatively low-cost way of making health care affordable to all and broadening the insurance pool to keep premiums down.

We should explore expanding Medicare, especially for long-term care so senior citizens and people with disabilities don’t have to impoverish themselves to qualify for Medicaid in order to afford extended stays in a rehabilitation center or nursing home.

We should also take steps to lower costs, such as allowing Medicare to negotiate lower drug prices with the pharmaceutical industry and accelerating the move away from traditional fee-for-service models toward accountable-care organizations and other innovative approaches that reward good outcomes rather than more services.

And more broadly, we must work to make the U.S. health-care system more seamless. There is no good reason for the level of disruption people encounter when they change plans today. That means making the benefits covered, degree of cost-sharing and other provisions the same whether your coverage is through Medicare, Medicaid or private insurance.

Much as I respect the passion of Medicare-for-all advocates and share their broader goals, single-payer is no panacea. We couldn’t muster the votes for single-payer nine years ago when we had a filibuster-proof 60 votes in the Senate and a 255-179 majority in the House. Even if we recapture control of Congress in 2018, our margins will be smaller. And of course, the Republican in the White House would veto any such legislation.

Just as important, single-payer is no policy panacea. Medicare is hugely successful and popular, but most beneficiaries purchase private supplemental insurance to reduce the burden of large out-of-pocket costs. The most prominent single-payer bill would eliminate all out-of-pocket costs for Medicare, a move whose astronomical costs would require tax increases at politically suicidal levels.

Moreover, most countries with universal coverage, including Germany, France, Switzerland and the Netherlands, do not have what we would define as single-payer, instead relying on private insurance as part of the mix.

Democrats can embrace a boundless vision for our health-care future without being trapped by a rigid model for how to get there. Instead, we should focus on increasing the number of Americans with comprehensive health insurance and lowering costs. Let’s be united on the goal of universal coverage, pragmatic on tactics and focused most of all on making a positive difference in as many people’s lives as possible.