So Republicans won enough seats to take control of the US Senate in January for the first time since 2006. Given their continuing opposition to the Affordable Care Act (aka Obamacare), is this an existential threat to the law’s survival, and what might we expect over the next two years?

The ACA’s lifespan has included three near-death experiences where the law’s life hung in balance. Recall Scott Brown’s 2010 election to the Massachusetts Senate seat that eliminated a filibuster-proof majority for Democrats. Remember the US Supreme Court’s 5-4 ruling on the ACA’s constitutionality in June 2012 – one changed vote would have repealed the entire law. Consider that a Mitt Romney win in November 2012, if accompanied by a Senate Republican majority, would have triggered near total repeal in 2013.

The Republicans’ capture of the Senate does not rival any of those threats for several reasons.

First, on January 1, 2014, the ACA’s benefits transformed from hypothetical to real. ACA repeal now would eliminate health insurance for more than 10 million formerly uninsured Americans, and disrupt coverage and benefits for tens of millions more, including Medicare enrollees. Repeal would also harm hospitals, insurance companies, and other powerful stakeholders who have learned to live with and, in many cases, profit from the ACA.

Second, while the 2014 Senate political map strongly favored Republicans, the 2016 map favors Democrats more strongly. In 2016, Republicans will need to defend 24 of 34 Senate seats at stake, unlike this year when they defended only 15 of the 36 seats up for grabs. The 2016 turnout in a presidential election will also be much friendlier to Democrats than 2014, with higher turnout among non-white and younger voters.

Senate and House Republicans may well advance legislation early next year to repeal the entire ACA knowing that an Obama veto will render the gesture meaningful only to a hardcore base that Republican leaders seem increasingly disinclined to appease. Unlike the 54 times in the past four years that the House voted to repeal all or part of the ACA, next time would be different. Nearly all Democrats would unite behind the law, and Republicans would splinter. Hard-core tea party regulars would rejoice, while members facing re-election in non-red states would rebel – especially as their Republican governors warn of state fiscal calamity at the prospect of repealing the ACA’s Medicaid expansions.

After the final failed effort to repeal the ACA is done, Republicans will initiate a search-and-destroy operation to eliminate any and every section of the ACA they can. While many worthy and meritorious provisions will be at risk, and some will fall, none will be mission-central to the two vital purposes of the ACA – to provide secure and affordable health insurance to millions of uninsured Americans and to improve the quality and efficiency of America’s woefully poor-quality and inefficient medical care system. Budget reconciliation, which requires only 51 votes and is not subject to filibuster, will be the likely legislative pathway – and spring 2015 will be the period of opportunity.

What provisions are in peril? Here’s my top list:

The Individual Mandate – requiring most Americans to purchase health insurance when they can afford it or to pay a tax penalty – first round of penalty payments, which are coming due this spring (bad timing). The insurance industry and ACA supporters will argue that repeal will increase premiums as younger and healthier individuals drop coverage. But Republicans have gone too far out on a limb to back down on this one.

Employer Responsibility (aka the employer mandate) – which requires larger employers to contribute when their otherwise uncovered workers obtain ACA subsidized health insurance. (The Congressional Budget Office estimates repeal would increase the federal debt over 10 years by about $150 billion.)

The Medical Device Industry Tax – which requires device makers to pay a fee, like all other major health industry stakeholders. (CBO estimates that repeal would increase the federal debt by $29 billion over ten years.)

The Medicare Independent Payment Advisory Board – established to limit Medicare cost growth when costs rise too high. Because of the sharp decline in Medicare’s rate of cost growth since 2010, the IPAB would not be called to duty until 2020 at the earliest.

The Center for Medicare and Medicaid Innovation – which funds promising approaches to improve quality and control costs, and can implement successful new models more rapidly.

The Patient Centered Outcomes Research Institute – the nation’s first substantial effort to compare medical treatments and diagnostics to evaluate their effectiveness with other approaches.

Public Health and Prevention Trust Fund – which disburses money for community-based preventive programs and initiatives across the nation, the ACA’s major investment in prevention and wellness.

Lots to say about each of these initiatives – just not now.

What’s not on the list? Here’s what I see:

Insurance reforms, including elimination of pre-existing condition exclusions and medical underwriting. Just about everybody hates insurers rejecting enrollees because of their medical histories – including the insurance companies.

Health Insurance Exchanges/Marketplaces. Despite predictions of failure, insurer participation in the federal and state exchanges jumped about 25 percent in year two.

Risk adjustment, reinsurance, and risk corridors. Though Republicans like to call these an insurance industry “bailout,” their favorite part of Medicare, called Medicare Advantage, uses these same tools to make that market work.

The Medicaid expansion. During the October 2013 federal government shutdown, Arizona’s Republican Governor Jan Brewer said ACA repeal would create a “budget catastrophe” in her state because of the Medicaid expansion.

Accountable Care Organizations. Even though the jury is still out, it’s one of the law’s most interesting experiments. Ditto Patient Centered Medical Homes.

Penalties on Hospitals for high rates of readmissions that took effect in 2012. It may and should be modified to avoid unfair harm to safety net hospitals – but this is one ACA provision that both parties appreciate.

Cuts in Medicare payments to hospitals, insurers, home health and hospices. In election years, Republicans attack these cuts that finance about 45 percent of the ACA’s total cost, and in non-election years, this line of attack disappears.

Closing the Medicare Part D “doughnut hole” (coverage gap) – not now, not ever.

Since the legislative debate over comprehensive health reform started in 2008, the process of passage and implementation has been straight out the Perils of Pauline. Another chapter is now opening – as the ACA settles more deeply into the national landscape.

John E. McDonough is a professor at the Harvard School of Public Health and the author of Inside National Health Reform.