One test of a nation-changing law is that it remains a centerpiece of American life and Washington’s pitched political fights long after the president responsible left office.

Franklin Roosevelt’s New Deal still supports millions of citizens every day 90 years after he signed the Social Security Act.

Lyndon Johnson’s Voting Rights Act is still hanging on, just, despite Supreme Court decisions that watered down its protections for minority voters. The law remains a lightning rod in political disputes six decades after its passage.

President Franklin Delano Roosevelt addresses crowds at Grant Field, in Atlanta, defending the New Deal, on November 30, 1935. Bettmann Archive/Getty Images

In the 15 years since Barack Obama signed the Affordable Care Act into law, Republicans have tried to repeal it, to invalidate it, defund it and get it thrown out by the Supreme Court. But the law has proven remarkably un-killable and has only grown in popularity as it’s become more deeply embedded in US life. But if Republicans succeed in ending some ACA subsidies, they could begin to throttle the law to death.

Now, Obamacare is again at the fulcrum of a bitter Washington battle, as Democrats seek to leverage the government shutdown to secure the extension of healthcare subsidies to prevent premiums under the plan from soaring.

They hope to extend subsidies originally enacted by th