To understand how this might work, it helps to understand a little bit about Senate procedure.

The Senate effectively requires 60 votes to pass most legislation, but Republicans hold only 52 seats. However, Senate rules allow for the passage of certain types of legislation using a process known as reconciliation, which requires only a simple majority. Republicans planned to use the reconciliation process to go it alone on both health care and tax reform.

But that process comes with conditions. There’s a ticking clock; the reconciliation instructions that allow for the passage of the health care bill expire as soon as the next budget resolution is introduced. And the process does not allow for the passage of legislation that raises the deficit outside the 10-year budget window via a simple majority.

This, for example, is why the tax cuts passed under President George W. Bush in 2001 were set to expire after a decade. For tax cuts to be permanent, they must be deemed “revenue neutral.”

That is where the American Health Care Act comes in: It would eliminate roughly $1 trillion in taxes used to pay for the additional spending in Obamacare. As a result, it would significantly lower the federal government’s tax revenue baseline. The baseline is an important figure in congressional budgeting, because it sets expectations for how much the government is projected, on paper, to spend and raise if current law remains the same.

The trick, then, is to make the health care bill’s tax cuts part of that baseline by passing them into law before a tax-reform package. This would provide Republicans with far more room to permanently cut taxes later in the year. In short, Republicans would be able to devise a tax bill that collects about $1 trillion less in revenue but that would still qualify as revenue-neutral under Senate procedure.

This is why Republicans put health care reform at the top of their agenda. Without the bill to reset the federal government’s baseline tax revenue, Republicans would be much more constrained when it came time to overhaul the tax code.