The list of provisions includes a clause, which many conservatives consider essential, that would defund Planned Parenthood and block federal money from helping to pay for insurance policies that cover abortion. Parliamentarian Elizabeth MacDonough also ruled out a six-month “lockout” period for people trying to buy insurance after they have let it lapse ― a key policy feature of the Senate bill that insurers say is vital to keeping markets stable.

In the ruling, a summary of which the office of Sen. Bernie Sanders (I-Vt.) posted, the parliamentarian’s office indicated that it would still be reviewing other parts of the Senate proposal ― including provisions that would allow insurers more flexibility to vary premiums by age or to offer plans that leave out benefits such as mental health and maternity care that current law considers essential.

And the parliamentarian hasn’t even had a chance to consider a new amendment, proposed by Sen. Ted Cruz (R-Texas), that would allow insurers to offer some plans not subject to rules guaranteeing coverage for people with pre-existing conditions.

Politically, the biggest blow for Republicans is the ruling that a provision prohibiting funds from being used to purchase insurance policies that cover abortion. That rider was key to House conservatives accepting their version of the legislation, and Freedom Caucus Chairman Mark Meadows suggested that, without that prohibition, the bill could not pass the House on the way back from the Senate.

“The elimination of the Planned Parenthood [funding prohibition] is very puzzling since it passed the parliamentarian’s scrutiny in the past,” Meadows told HuffPost Friday afternoon, “but today’s ruling as it relates to the life issue will make passage almost impossible.”

The ruling matters because Republicans are trying to pass legislation through the budget reconciliation process, a special procedure in which measures are not subject to a filibuster in the Senate. That makes it possible to pass a bill with just 50 senators rather than 60, with the vice president breaking the tie ― something essential for Republicans, because they have only 52 seats and are not trying to pass their bill with Democratic support.

But if reconciliation makes it possible to pass a bill with fewer votes, it also imposes strict rules on what a bill may include. Legislation must have a significant economic impact and cannot merely change policy ― otherwise it is subject to 60 votes. (This is called the “Byrd Rule,” named after former Democratic Sen. Robert Byrd of West Virginia.)

The parliamentarian is the one who interprets rules. If the parliamentarian decides a provision does not conform to the guidelines for reconciliation, Democrats can (and surely would) demand that the provisions be subject to normal voting procedures ― in other words, subject to a filibuster that would require 60 votes to overcome.

“The parliamentarian’s decision today proves once again that the process Republicans have undertaken to repeal the Affordable Care Act and throw 22 million Americans off of health insurance is a disaster,” said Sanders, who is ranking member of the Senate Budget Committee.

The parliamentarian’s ruling is not the end of the story. Republicans could modify language in their bill, in the hope that with some small tweaks it would pass muster. Or they could decide to vote on legislation other than the Better Care Reconciliation Act, which is the bill GOP leaders submitted for consideration.

Additionally, the parliamentarian isn’t the final arbiter of what the Senate may consider in reconciliation. It’s the presiding officer, who in this case would likely be Vice President Mike Pence. The presiding officer could simply ignore the parliamentarian’s guidance ― a move that conservatives like Cruz have suggested Republicans consider, even though it would flout Senate traditions and other Republicans have hinted they would not support it.