But the biggest hurdles for Republicans have centered on the vexing policy questions that pit the political imperative to match the benefits of the Affordable Care Act against their ideological opposition to government involvement in the market. How much will it cost? How will they pay for it? How many people will be covered? And what will happen to the parts of the current law that people like the most?

Taxes

Democrats paid for the new benefits and programs in the Affordable Care Act by raising taxes on wealthy individuals, medical devices, even indoor tanning salons. They also capped the tax deduction for the most expensive employer-sponsored insurance plans—a provision that became known as the “Cadillac tax.”

Republicans denounced all these new charges, and conservatives have demanded that they be eliminated right alongside the repeal of the broader law. But other lawmakers want to keep at least some of the taxes in place to pay for the policies in the GOP replacement plan, like funding for high-risk insurance pools and tax credits for expanded health savings accounts. “The revenue is essential,” Senator Bill Cassidy of Louisiana told reporters as he introduced a compromise plan last month, explaining that without revenue from Obamacare’s taxes, Republicans can’t hope to fulfill President Trump’s own request for a healthcare plan that provides “insurance for everybody.”

Yet the hardline House Freedom Caucus has already vowed to oppose any bill that keeps the ACA tax hikes. One option under consideration is for Republicans to scrap the current regimen of taxes but replace them with a version of the Cadillac tax that Congress already repealed as part of the ACA. The policy under discussion, according to The New York Times, would limit the tax break that allows people to deduct the cost of health insurance off their federal taxable income. That’s a proposal that health economists have advocated for years, but it has been nearly impossible to implement because of the popularity of the tax break; the scaled-back Cadillac tax was so unpopular that Democrats eventually agreed to get rid of it.

Deficit Impact

The fate of Obamacare’s taxes is directly related to another crucial question for Republicans: How much will their bill cost? The new tax revenue meant that that Affordable Care Act actually shrunk federal deficits over a decade, and because of that, the Congressional Budget Office has projected that previous GOP repeal bills would have raised the deficit by several hundred billion dollars. Republicans have disputed these estimates, but for a party that attacked former President Barack Obama for presiding over a steep increase in the debt, it’s a big political problem. In January, Senator Rand Paul of Kentucky cited the deficit impact as a reason he voted against the budget resolution that Republicans passed to lay the groundwork for repeal. And according to The Hill, a House committee is pushing back its consideration of repeal-and-replace legislation because some elements of the bill received a poor score from the CBO.