Amidst the partisan rancor and the unusual tilt toward questions on civility during the second and third presidential debates, Hillary Clinton and Donald Trump drew the attention of health experts when they articulated their path forward for health policy in America.

Responding to questions about the lack of affordability in the Affordable Care Act, the candidates detailed how they would address the increasingly glaring flaws in President Obama’s signature policy achievement. Mr. Trump, who called the ACA a “disaster,” has pushed for repeal of the law. He wants to replace it with block grants for Medicaid and the sale of health insurance across state lines.

Secretary Clinton has emphasized the positive aspects of the ACA, including safeguards to ensure that insurers cannot deny coverage because of an applicant’s preexisting conditions. She has argued that changes must be made at the edges of the existing law.

As important as these discussions have been for providing the American public details about each candidate’s future plans in the health policy arena, they were also significant for the option they ignored – the possibility of universal health coverage in America.

The ACA certainly brought us closer to universal coverage, a system where the government typically pays for basic health care services for everyone. However, the fact that a true national health insurance system didn’t even warrant discussion by the major party candidates is surprising – or at least should be. The United States remains one of the only advanced industrialized democracies in the world without universal coverage.

While this in and of itself is not a problem, the United States also spends more on health care as a percentage of GDP than any other advanced country in the world and has worse health outcomes – with lower life expectancy, higher infant mortality and higher obesity rates than comparable countries like Australia, Canada, the United Kingdom, Germany, France and Japan.

It is also surprising because Bernie Sanders, running on a platform that included universal coverage or what he called Medicare for all, generated massive grassroots support and energized the millennial population that makes up an increasing percentage of the electorate.

Given these facts, it is important to ask: Why isn’t universal coverage through a national health insurance system even being considered in America? Research in health policy points to three explanations.