Congressional Republicans are considering a lightning-strike rollback of Obamacare early next year to kick off the Donald Trump era, but first they have to agree on a plan limited enough to hold their caucus together.

Republicans won’t have much room for error to successfully repeal Obamacare, a top campaign promise of Trump and congressional Republicans. Even if they delay the repeal to allow more time to come up with a replacement, there will be pressure to use the legislative maneuver to push through other top GOP priorities, such as defunding Planned Parenthood.

But Senate Republicans would have to keep unified the 52 senators they expect to have when the new Congress convenes Jan. 3.

The Republican plan would take advantage of reconciliation, a budget-related mechanism to circumvent the 60-vote threshold in the Senate and prevent Democrats from being able to block legislation on their own. By striking early, the GOP could set itself up to invoke the same procedure again later in the year on a broader range of targets, including tax cuts.

The quick-strike bill, like one vetoed earlier this year by President Barack Obama, H.R. 3762, would likely set what amounts to an expiration date for the law’s financial underpinnings, leaving Congress to act at a later date on any replacement plan. That’s because more than six years after the law’s passage, Republicans still don’t have a consensus on how to replace Obamacare.

But passing something in Trump’s first 100 days would allow Republicans to claim a big win early on, and conservatives are demanding the GOP deliver quickly.

"In order to give a clear and unambiguous message there’s a new occupant in the White House, one of the first things that should be done after the oath of office is passage of a bill through reconciliation repealing Obamacare and defunding Planned Parenthood," Representative Trent Franks, an Arizona Republican, said Monday in an interview.

Franks, chairman of the House Judiciary subcommittee on the Constitution, said he worries that some in Congress may seek more time to pass a bill. But he said the bill should be passed "almost the first moment after the oath of office." Congress needs to send the message that when people vote based on promises made during a campaign, "that their votes will matter," he said.

House Majority Leader Kevin McCarthy told reporters Tuesday at a Washington Post breakfast that the first 100 days of Trump’s administration may include action on an Obamacare repeal, although "repealing is easier and faster" than replacing.

Having a "transition period" after a vote to repeal Obamacare would create a deadline for Congress to pass a replacement, he told reporters later Tuesday.

"If you have a date certain that something is going away" lawmakers will be motivated to pass a replacement, McCarthy said. Democrats who try to obstruct a replacement would risk being blamed for allowing Obamacare to lapse without a new plan, he said.

John Cornyn of Texas, the No. 2 Senate Republican, said Monday that a Obamacare repeal is "going to be high on the list right when we come back."

"It will be early, because we have to get that done," Cornyn said. "January would suit me just fine." He said Republicans may use the reconciliation procedure again later in the year to push through other matters, such as a tax overhaul.

Lamar Alexander, chairman of the Senate Health, Education, Labor and Pensions Committee, predicted during an interview with reporters that it would ultimately take "several years" to fully move to a new system with less federal control. He said that while Republicans can do some things with reconciliation, they’d ultimately need 60 votes.

"We need to gradually move those decisions back to states and to individuals and do it in a way that does no harm to people today," the Tennessee Republican said.

"If we want a lasting solution, eventually we’re going to have to have 60 votes in the Senate to get it."

While a lightning-strike bill could be used for other priorities Republicans agree on, House Budget Chairman Tom Price of Georgia predicted in a recent interview it would be focused on something similar to the Obamacare repeal bill lawmakers have already passed because expanding it would require more time for committees to work.

"There is an opportunity there," said Price, who Trump named Tuesday morning to be his secretary of Health and Human Services. "All this has to go through the process obviously."

The idea for a lightning-strike bill has been percolating among Capitol Hill Republicans since long before the election, and it’s sure to provoke howls from Democrats.

But there’s not much they can do under the rules, beyond kick up a fuss. Senate Democrats’ leader-in-waiting, Chuck Schumer of New York, has said in several interviews that Republicans will rue the day they roll back the health law.

Representative Gerry Connolly, a Virginia Democrat on the Oversight and Government Reform Committee, said the law has worked in many important ways, including insuring millions of people and banning the denial of coverage for pre-existing conditions.

"But it’s not about facts or data or performance. It’s about political promises, and what they said they would deliver," he said, adding that he doubts Trump and congressional Republicans could backtrack now politically.

To pull off a lightning strike, Republicans would have to pass a budget resolution first for the current budget year, which can take a week or two even if they are in agreement on what it should say. That resolution would set budget targets for the bill to follow. Then the committees would have to push through the actual repeal bill.

Republicans will also face internal fights if they end up keeping much of the law in its current form.

"When we all run for office, we run on repeal and replace with a free-market alternative," said Representative Dave Brat, a conservative member of the Freedom Caucus from Virginia. "We did not run and say: ‘Let’s kind of soften this failed experiment down a little bit and keep most of the elements of socialized, top-down central planning in health care, along with 20 to 50 percent premium increases, and mandates forcing you to buy products by the federal government.’"

"We don’t need to be nasty, but we need to be rational and principled. And if we do not move forward with what we promised, the American people will rightly judge us as a failure, and a moral failure, as well, for not keeping our word," said Brat.

But already there are some Republicans who are concerned about the possible scope of a reconciliation effort now that whatever they pass could actually become law.

Representative Dennis Ross, a Florida Republican who is a senior deputy whip, said Tuesday, "In my view, the repeal is not nearly as important as replacement."

"To just say ‘repeal everything, and the mandates, without a replacement,’ then what?" he asked. "I don’t think we can do a repeal without a replacement. People are already in the system."

One House centrist, who didn’t want to be identified by name in order to speak more freely, confirmed several members are voicing their opposition to leaders about voting again to defund Planned Parenthood in the reconciliation package.

But Speaker Paul Ryan suggested that GOP leaders plan to push ahead. During his most recent Capitol news conference on Nov. 17, he said, "We’ve already shown what we believe with respect to Planned Parenthood. We put a bill on President Obama’s desk in reconciliation. Our position has not changed."

Republican leaders are also talking with Trump about how exactly to move forward.

"Obamacare has hurt families across the country through higher costs and less choice, and they made their disgust with the law known by voting for a candidate who ran on repeal," said Ryan spokeswoman AshLee Strong.

"Speaker Ryan is in near-daily communication with President-elect Trump and Vice President-elect Pence about the agenda for next year," she added. "We will share more when we have it."

Don Stewart, a spokesman for Senate Majority Leader Mitch McConnell of Kentucky, said they have nothing to announce yet on the schedule.

“This continues to be a top priority for the Senate Finance Committee, which has kept a steady pace with its efforts to replace Obamacare with common-sense reforms that will lower costs and increase choice," said Julia Lawless, spokeswoman for Finance Chairman Orrin Hatch of Utah. "The chairman is working with members to find the best way to move forward and is confident Congress will be prepared to act quickly next year.”

The reconciliation process can also be used on tax bills and to raise the federal debt limit, which must be done sometime in mid-2017. The last time Republicans had control of the House, Senate and the White House during George W. Bush’s administration, they pushed through an assortment of items via reconciliation packages, affecting taxes, Medicare, Medicaid, and numerous other programs.