Senator Robert Byrd helped save the Affordable Care Act once already. In December 2009, the wizened West Virginia Democrat overcame fragile health to cast a crucial vote for the act’s passage. It was one of the last votes in the career of the Senate’s longest­-serving member: Just weeks after President Obama signed the Affordable Care Act into law, Byrd died at age 92.

Now, nearly seven years after his death, Senator Byrd may ensure that the Affordable Care Act, also known as Obamacare, lives another day. One of Byrd’s many legislative accomplishments over a half­century in the Senate was the eponymous “Byrd rule,” which governs the process of budget reconciliation. Republicans on Capitol Hill are trying to use the reconciliation process to repeal and replace the Affordable Care Act. The Byrd rule stands in their way.

Reconciliation is a fast­track process that allows budget-­related legislation to pass the Senate without the prospect of a filibuster. The Byrd rule prevents reconciliation from being used to pass any measure for which the budgetary effects— “changes in outlays or revenues” — are “merely incidental to the non­-budgetary components.” Republicans know they lack the 60 votes to break a filibuster in the Senate, so they designed their repeal­-and-­replace bill to satisfy the Byrd rule’srequirements. Yet there is a surprising flaw in their design — one that has so far drawn little notice, but that Senate Democrats will surely seize on.

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