Though he’s not labeling 2015 as the “crucible” for the Affordable Care Act, Andrew Evans of the Washington Free Beacon details several challenges for the health care reform law in the new year. One of them involves a change in federal payments linked to Medicaid.

One of the more obscure parts of Obamacare was an increase in the amount that primary-care doctors get paid for seeing patients with Medicaid, the government’s health-insurance program for the poor.

This fee increase was an attempt to patch a much bigger flaw with Medicaid. This program systematically underpays doctors for seeing patients—typically poor children and mothers—who are insured through it. The incentive structure encourages the states, who actually run the program largely with federal dollars, to cut the reimbursement rate for doctors, and the result is that Medicaid paid in 2012 about 66 cents for every dollar paid by Medicare, the federal insurance program for the elderly, and closer to 50 cents for every dollar paid by private insurance. (And remember—these are averages; some states pay doctors far, far less for serving Medicaid patients.)

The result is predictable: Doctors are reluctant to accept Medicaid patients because they simply don’t get paid enough.

To solve this problem, Obamacare gave states the money to make Medicaid pay the same as Medicare. This extra money was especially important because Obamacare expanded Medicaid while leaving its structure in place. The money basically greased the system, making it easier for patients with Medicaid to get in to see a primary-care doctor.

This new money expired Dec. 31, since Congress did not extend it in its massive spending bill passed earlier that month, and as a result primary-care doctors seeing patients with Medicaid will see their pay cut significantly in 2015. This pay cut will affect a large number of the newly insured under the law: About 70 percent of the net increase in people with insurance in 2014 was due to the Medicaid expansion.

This payment cut means that at least some people with Medicaid will have trouble getting in to see a doctor. Obamacare’s cogs will be running a little less smoothly in the new year.