Congressional Republicans have long boasted that once they claim the reins of power, they will act quickly and decisively to roll back what they view as the most onerous piece of President Obama’s domestic agenda: the Affordable Care Act.

But their actions starting Tuesday to end Obamacare will be far less sweeping, at least initially, than a full-blown repeal of the law.

Democratic opposition and complex Senate rules mean that core pieces of the 2010 health-care overhaul are likely to remain, including the legal framework for the individual mandate and pieces of the state exchanges the law created. Furthermore, President-elect Donald Trump has vowed to preserve other key aspects, such as a ban on insurers denying coverage because of preexisting conditions and a requirement that insurers cover children under 26 on their parents’ plans.

And while Republicans are determined to rapidly repeal as much of Obamacare as they can, they have not settled on a replacement plan or on when that plan should take effect.

“We will move right after the first of the year on an Obamacare replacement resolution,” Senate Majority Leader Mitch McConnell (R-Ky.) said during a December news conference. “Then we will work expeditiously to come up with a better proposal than current law, because current law is simply unacceptable and not sustainable.”

(Daron Taylor/The Washington Post)

[New push to repeal Obamacare ignites old GOP tensions]

According to the latest estimates from the Department of Health and Human Services, the resulting jumble is likely to have an unpredictable and messy effect on the insurance marketplace, jeopardizing the health coverage of the 20 million people who have gained it under the Affordable Care Act.

The rush to immediately chip away at Obama’s regulatory and domestic policies through the complex process known as budget reconciliation could create months of messy GOP infighting. The plan to vote now on repeal and work out the details later means Republican leaders will be slogging through the difficult process of writing a health-care replacement while simultaneously trying to scale back regulations in areas such as clean air and immigration, and possibly tackling a tax-code overhaul. It will be the first real test of how effective the GOP-controlled Congress will be.

A wild-card element is where Trump stands on the details of replacing the ACA — he has said more about the pieces he would like to keep than his ideas for remaking it. Trump’s stance may be clarified after Vice President-elect Mike Pence — a leader in the Obamacare repeal effort during his time in Congress — joins House Republicans to discuss the ACA on Wednesday at their first weekly gathering of the year.

Democrats warn that a frenzied push to dismantle Obama’s legacy could leave Republicans without any hope of getting the bipartisan support necessary to push through other parts of the Trump agenda, including the replacement bill and a pricey infrastructure project.

House Minority Leader Nancy Pelosi (D-Calif.) suggested in a conference call Monday afternoon that the reason Republicans are not moving immediately to replace the health-care law is because they can’t. “The reason they can’t make a proposal is because they don’t have the votes,” Pelosi argued.

The budget legislation containing repeal — which leaders plan to introduce in the Senate as early as Tuesday — will be a bare-bones outline of GOP spending priorities. It will also include very general instructions for committees in the House and Senate to write the actual bills repealing the law. The budget resolution can be passed by a simple majority, but McConnell is required to allow lawmakers to offer a nearly unlimited number of amendments in a process, known as a “vote-a-rama,” that could take up to a week to complete.

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[How to pay for Trump’s trillion-dollar agenda? Republicans aren’t saying.]

Once the resolution is passed by the Senate, the House is quickly expected to follow suit. That is when the committees — the Ways and Means Committee and Energy Committee in the House and the Finance Committee and Health, Education, Labor and Pensions Committee in the Senate — will start work.

The panels are charged with crafting the repeal legislation with an eye toward the budget rules, which will determine how many votes the language needs to be approved. The goal is to craft a bill that can pass muster with House conservatives while still being able to meet the 50-vote threshold in the Senate. The sticking point is this: To be eligible for a simple-majority vote, the language must be related to taxes or spending or somehow add to the long-term federal debt.

Once the committees approve their versions of repeal — something aides expect may happen in February or March — the House would vote on the entire repeal package before sending it to the Senate, where the chamber’s parliamentarian will pick through the legislation with a fine-toothed comb. The parliamentarian has the authority to throw out any elements that violate budget rules before the bill comes up for another vote in the Senate. If the parliamentarian rules against Republicans, it is at this point that Democrats would probably have their best chance to defeat the measure or otherwise alter it. Incoming Senate Democratic leader Charles E. Schumer (N.Y.) has pledged to block all replacement efforts.

In all, the repeal process could easily last into early spring or later, aides predicted.

The effort is expected to follow a path similar to the one Republicans blazed in 2015 with the repeal measure ending in an Obama veto, according to several GOP leadership aides. Conservatives openly touted that bill as a “dress rehearsal” for the future.

That effort used the budget process to eliminate the penalties for individuals who do not buy health insurance and repealed the authority of the federal government to run health-care exchanges, rendering the parts of the ACA intended to expand private insurance coverage essentially useless.

Heritage Action for America called that effort a “trial run” in a July 2015 memo, one that would “reaffirm the Republican-controlled Congress’s commitment to sending a bill repealing Obamacare to the president’s desk in 2017 — when it will hopefully be signed into law.”

Many conservatives, including Sens. Ted Cruz (R-Tex.) and Marco Rubio (R-Fla.), criticized that effort, saying it did not go far enough. The two lawmakers, then candidates for the GOP presidential nomination, eventually voted for the chance to gut the health-care law, but some conservatives are still frustrated that a repeal bill can only go so far because of the budget rule constraints.

Congressional aides declined to give specific details of any planned changes until lawmakers meet and the committees begin their work. But key lawmakers and aides said the new repeal bill may not differ much from the eight-page 2015 bill.

For instance, that bill eliminated the tax penalties, tax credits and cost-sharing subsidies central to the ACA’s individual mandate to purchase health insurance. But because the budget rules do not allow for unrelated language, the mandate itself was not repealed.

Also left intact by the 2015 bill: HHS regulations that created national insurance standards defining the benefits that must be included in ACA health plans, as well as limits on how much insurance companies can vary their pricing of those plans by age, gender or other factors.

In an updated memo issued last month, Heritage Action said the 2015 measure should be “seen as a floor, not a ceiling, for what the Republican Congress and President Trump can accomplish” and suggested that a simple majority of senators could vote to overrule the Senate parliamentarian’s decisions on which provisions are considered “extraneous” or not permitted under the budget rules.

“There are no more excuses,” Heritage Action said, sounding an ominous note for Republicans who have long promised to deliver on their years of repeal rhetoric.

But politics, not Senate rules, might be the more significant obstacle to a comprehensive Obamacare repeal. One unanswered question is whether the repeal bill will include a key provision of the 2015 bill: the defunding of Planned Parenthood.

Republican leaders have not explicitly committed to pursuing a defunding of Planned Parenthood, and Trump has given mixed signals on whether he wants to target the organization.

But conservatives consider it a top priority to block Planned Parenthood from accessing Medicaid funding and other federal grants — and they may use the repeal bill to do so. Taxpayer funding for abortions is already illegal, because of a spending restriction that has been in place since 1976. But Planned Parenthood provides a host of other health-care services for women, including cancer screenings and gynecological exams.

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