Republicans have already rehearsed how they'd repeal Obamacare, and they have a script for replacing it.

Now with President-elect Donald Trump as their ally in the White House, the question is whether they'll get stage fright.

There's broad consensus that simply ditching the Affordable Care Act and stripping up to 20 million Americans of their insurance would be a political disaster for Republicans, opening them up to damaging attacks from Democrats in 2018. So if GOP members of Congress follow through next year on their longstanding promises to repeal the healthcare law, they'll face two basic options.

They could pass a budget reconciliation bill that gradually sunsets the law, preserving its subsidies and Medicaid expansion for a time while they agree on a replacement. They've already got a script for that approach, after passing a reconciliation bill last January which President Obama vetoed.

Or Congress could pass a replacement plan right away by coupling it with a repeal bill, although it's questionable Republicans could find consensus in such a short timeframe.

"It becomes a political question of can you repeal the Affordable Care Act without something ready to go behind it," said Lanhee Chen, a Stanford University professor and former advisor to Mitt Romney. "My instinct there is no you can't, you need to have some kind of backstop for it."

It's too early to tell exactly what timeline Republicans will choose, as members collect themselves after Trump's surprise victory on Wednesday. But two things are certain, according to Rep. Kevin Brady, chairman of the powerful Ways and Means Committee: the House will vote on a repeal bill and it will move forward with the replacement plan laid out by Speaker Paul Ryan last year.

"We are going to repeal the bill in the House, there's no mistake about that," Brady told the Washington Examiner. "And we'll also move forward with the step-by-step solution we identified in 'A Better Way.'"

Trump hasn't explicitly backed the Ryan plan, but the proposal does contain some similarities with ideas Trump suggested during his campaign. Chief among them is enabling insurers to sell plans across state lines, which Republicans say is a step towards greater competition.

The Ryan plan would also replace Obamacare's subsidies with refundable tax credits and end its Medicaid expansion, gradually phasing down the extra federal funds to states. States could choose to receive their remaining Medicaid dollars either through block grants or per capita allotment.

It retains some of Obamacare's most popular provisions, including the provision that lets dependents stay on their parents' plan to age 26 and ensures people with preexisting conditions get coverage.

If Republicans work off the Ryan proposal, but agree they want a smooth coverage transition for people with Obamacare coverage, they have to spell out in more detail exactly how they would achieve that goal. And reaching consensus on all of it will be a challenge. All the major committee leaders back the Ryan plan, but they'd have to get most of the rank-and-file in line too.

Brady said he and other leaders will sit down with the Trump transition team in the coming weeks to map out a strategy.

"To be determined," Brady responded, when asked about their approach. "We will huddle with the Trump administration about their priorities on Obamacare and timetable."

If Trump is interested in rolling back or changing the healthcare law on his own, there are a number of things he may be able to do without help from Congress.

He could refuse to provide cost-sharing subsidies to insurers, which is the subject of a House lawsuit against the Obama administration. He could also try to prevent insurers from getting payments for their marketplace losses through two programs known as reinsurance and risk corridors. And he could provide states with more flexibility for how they conduct their Medicaid expansion programs.

In contrast, it will be a lot harder for hundreds of members of Congress to agree on approaches to health reform. Besides just agreeing on a replacement plan's provisions, Republicans will also have to agree on how to pay for the refundable tax credits that would ensure poor people can afford to get coverage, a tricky question the Ryan plan doesn't address. And the pots of money are limited, experts say.

One funding mechanism could come through capping the tax exclusion for employer-sponsored coverage. Savings could also be achieved by block-granting Medicaid and repealing the healthcare law's spending on subsidies and Medicaid expansion, as the Ryan plan proposes.

But for now, Republicans are just beginning their discussions over how to approach Obamacare, the law they've tried to repeal for six years. It's a situation they've never yet been in, as Obama has refused to terminate any of his law's signature provisions.

Chris Jacobs, a former GOP healthcare staffer and founder of Juniper Research Group, said "nobody knows" exactly what's going to happen in January.

"I've gotten people on the Hill emailing me saying 'what do we do now,'" Jacobs said. "People were saying Democrats didn't have a plan to deal with a Trump administration. Neither do Republicans."