Republican health care plans: Understanding the 'Byrd Bath'

(CNN) Even as they still search for the votes, Republicans are moving swiftly toward a vote to overhaul the Affordable Care Act, but a weedy, Senate rule could still change the bill even more.

Before Republicans vote on their plan to replace Obamacare, Republican and Democratic staffers continue to discuss changes to legislation with the Senate's parliamentarian, the chamber's adviser on interpreting its rules and protocols, so that any health care proposal undergoes the so-called "Byrd Bath."

Nope, not that kind of "bird bath."

Let's back up.

The Senate is using a process known as budget reconciliation to try to pass their health care bill. Reconciliation allows them to pass a bill with just a simple majority (51 votes), but the process has a strict set of rules. Under reconciliation, Republicans have to prove that everything they are including in their Obamacare repeal bill has an impact on the budget and not just an "incidental" one (more on that in a moment).

This is where the Byrd rule comes into play. It's named after the late Democratic Sen. Robert Byrd of West Virginia, who came up with the rule to stop either side from abusing the reconciliation process and trying to use it to just pass legislation that bypassed a filibuster. Under the Byrd rule, you have to prove the following to include a provision in reconciliation:

1. Supporters of the proposal have to prove that the bill in question either increases revenues or reduces spending
2. That those changes are not merely "incidental"
3. That all the changes are within the jurisdiction of the committees outlined in the reconciliation instructions. In this case that is the finance committee and the health, education, labor and pensions committee.
4. Senators for their proposal have to achieve at least the same amount of savings as the House bill did. In this case, it is $133 billion over ten years. And you have to hit the same targets in the 1-year and 5-year windows.
5. The proposal cannot have any impact on Social Security.
6. The provision must not increase spending or decrease revenues outside of the budget window if you want it to be permanent.

This week, Republicans and Democrats will argue about those weedy rules. They will literally debate behind closed doors with the parliamentarian why something complies or not. Then, at some point, the parliamentarian will ultimately decide which provisions in the Senate health care bill comply with the Byrd rule.

Here is why that process matters.

The Senate health care bill could undergo changes in the Byrd bath. It's possible some of the provisions will be challenged. Some provisions could possibly be taken out of the GOP health care bill before it gets to the floor and others could be challenged once the bill is on the floor.

That could also have a major impact on who votes for this bill.

One of the provisions that outside congressional experts have raised concerns about is the one-year defunding of Planned Parenthood. Conservatives say they need the provision to be included in order to vote for the bill, but there are questions as to whether that proposal is Byrd compliant.

The provision survived the Byrd bath in 2015, but each time the review process is different.

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Another thing to keep in mind is that as Senate Majority Leader Mitch McConnell tries to win 50 "yes" votes, some of the regulatory reforms -- like Sen. Ted Cruz's amendment to loosen regulations on what plans insurers can offer -- could run into problems with the parliamentarian.