When faced with a tough question about nearly any aspect of the health bill moving through Congress, Republican officials like to mention their plan’s other “prongs.”

In a briefing Tuesday, White House press secretary Sean Spicer cited the prongs again and again. Paul Ryan, the House Speaker, is fond of mentioning them. So is Tom Price, secretary of Health and Human Services. They say the bill needs to be understood as part of a larger strategy of reforming the health care system, not a piece of legislation that, alone, can achieve their goals.

Details about the second and third prongs of the strategy are still sketchy, but some ideas have begun to emerge. This week, Price and Seema Verma, the administrator of the Centers for Medicare and Medicaid Services, sent a letter to governors welcoming them to submit applications to waive normal Medicaid rules, and add policies like work incentives and premiums. Such changes to regulations and standards are said to be Prong No. 2.

As for Prong No. 3? Members of the House have said they will soon take up bills that deal with medical malpractice and antitrust protections.

Here’s why the prongs are crucial to the effort to roll back the Affordable Care Act: Republicans have chosen to pass their health reform bill using a special budget procedure that limits the policy changes they can make. That means that many of their key policy promises made over the past few years — and even days — can’t be achieved in the bill.

Trump’s promise to promote health insurance sales across state lines? Not in the American Health Care Act. Price’s commitment to loosen burdensome benefit rules for private health plans in Obamacare? Also not in the bill. Ryan’s favored policy of high-risk pools? Not there either. The goal of giving states more flexibility to run their Medicaid programs according to local conditions? Barely.

There is some debate among Senate experts about exactly what sorts of insurance regulations will be allowed in a bill passed through the special budget procedure. Such bills, which cannot be filibustered and thus can pass with only 50 Senate votes (along with Vice President Mike Pence’s tiebreaking vote), must adhere to the so-called Byrd rule.

Named after Robert Byrd of West Virginia, who was the longest-serving senator in history, the rule says that senators can stop a bill under this special procedure if it could significantly increase the federal deficit over the long term or if it’s an “extraneous matter” to the federal budget. There are many complex details, which is why there is uncertainty about what counts. The House staffers who wrote the American Health Care Act apparently felt that changing the ACA’s requirement that all plans cover 10 basic categories of benefits would break the rule. (But, for example, they believed that changing the rules for how much insurance companies could charge older customers was OK.)

Alone, the American Health Care Act’s effects don’t match particularly well with favorite Republican talking points about health reform. The bill doesn’t do much to lower insurance premiums or to improve competition in insurance markets. It doesn’t allow customers to choose a customized health plan that is “right for them,” though it would allow insurers to sell products with slightly higher deductibles.

That’s why Republicans need the other prongs.

Those prongs will not necessarily be easy to, let’s say, thrust into action. Though there is some latitude for the Department of Health and Human Services to change regulations under the Affordable Care Act, not everything on the GOP wish list can be achieved through executive action alone. The minimum benefit package, which critics say makes insurance more expensive than it should be, is clearly specified in the ACA.

So is the requirement that insurers offer plans at the same prices to healthy and sick customers alike, a major impediment to creating high-risk pools that would cover sick customers. Price and his staff can make some changes on the margins. And a long-standing Medicaid waiver program can allow some customizing of state programs, but only through a detailed application and approval process. Major structural changes will take legislation.

On the legislative side, Republicans are hemmed in by their narrow Senate majority. Democrats have so far taken a hard line against Republican efforts to dismantle the ACA, and that means that any health care bill not passed through the special budget procedure will take 60 votes in the Senate to overcome a filibuster.

That means such bills will need every Republican to vote for them, plus the votes of eight Democratic senators. It seems hard to imagine that eight Democrats would want to vote for a law that strips away all Medicaid requirements for states in favor of maximum flexibility. That means that Prong 3 may be the hardest to achieve, unless Republicans are willing to tear up the filibuster or Byrd rule, changes that could have wide-reaching implications.

And what of the “prong” metaphor itself? It’s hard to know what Republicans may be picturing as they evoke the three-prong strategy. But people’s suggestions on Twitter include an electrical plug, a trident and a pronghorn.

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