Bangladesh, Sept. 25 -- The latest fight over Obamacare is being presented in Washington as another familiar partisan battle. But beneath the political rhetoric lies a more consequential question: how much taxpayer-funded healthcare spending is vulnerable to fraudulent or unauthorized enrollment, and how aggressively should the government respond?

That question has gained new urgency after the Centers for Medicare & Medicaid Services (CMS) announced that it had canceled approximately 315,000 Affordable Care Act Marketplace enrollments covering more than 760,000 individuals. CMS estimates that the action could return roughly $2.2 billion in taxpayer-funded advance premium tax credits.

The administration has described the cancellations a...