For the fourth day in a row, the Arkansas House of Representatives has refused to approve the yearly appropriation for its Medicaid program, dubbed the “private-option.” If the legislature continues this refusal and reverses its decision to expand Medicaid under Obamacare, state and federal taxpayers will save billions of dollars, making the Little Rock legislative battle the most important spending fight in the country.

Last spring, Arkansas made headlines for adopting a “free-market” alternative to Medicaid expansion. Instead of expanding using the traditional Medicaid model in which the federal and state government would directly fund enrollees’ care, Arkansas decided to provide subsidies to 250,000 new enrollees, so that they could purchase private health insurance through the bureaucratic exchanges created under Obamacare. By using private insurance, supporters claimed, Arkansas would be able to provide individuals with insurance coverage and protect them from the broken Medicaid system that fails to provide “significant improvements” to enrollees’ health.

Medicaid expansion will cost the federal government $800 billion over the next 10 years if all states expand their qualification thresholds for the program as Obamacare’s architects want. (Currently, only half of the states have obliged.)

Arkansas’ expansion is actually even more expensive than the traditional expansion model envisioned by President Obama and Health and Human Services Secretary Kathleen Sebelius. According to the Congressional Budget Office, private insurance actually costs 50 percent more than traditional Medicaid coverage. Earlier this month, Arkansas Gov. Mike Beebe, a supporter of the private option plan, acknowledged that the plan costs the federal government—read taxpayers—more. Under the conservative estimates from the state, Arkansas’ expansion will cost $20 billion over the next 10 years.

Arkansas’ actions could affect other states. Following its expansion last year, Iowa, Michigan, and Pennsylvania expanded their Medicaid programs using a private-option model costing federal taxpayers billions more. Defunding Medicaid expansion in Arkansas would likely stop the wave of expansion, saving even more public dollars.

If opponents of the private option are successful, Arkansas will do far more to help federal taxpayers this month than anything coming from Washington.