The Congressional Budget Office has underestimated Medicaid spending by billions of dollars every year for some time now and a new law that reduced illegal immigration in Florida may explain why.

Since 2000, the CBO has underestimated an average of $15 billion a year of Medicaid spending, while often overestimating Social Security and Medicare spending. The latest CBO budget outlook bumped up Medicaid spending estimates yet again, this time by another $50 billion over the next 10 years. But judging by its recent performance, the new projections will still be too low.