Washington (CNN) Senate Democrats are issuing a new warning to Republicans plotting a quick repeal of Obamacare next year: Don't count on us to help replace it.

"It they break this, they own it," said Sen. Patty Murray, who will be the third-ranking Senate Democrat in the new Congress. "They have failed to come up with any plausible way to provide care and health care insurance for so many people. If they take it away, they better tell us how to fix it because they broke it."

The strong words indicate the challenges ahead for GOP leaders and the Trump administration as they plan an immediate assault on President Barack Obama's signature legislative item. Behind the scenes, top Republicans are plotting on moving forward with a budget plan unusually early -- in January -- in order to allow them to circumvent a Democratic filibuster in the Senate and repeal much of Obamacare on a straight-party line vote around the time Trump is sworn into office.

But to replace Obamacare under the Senate rules, Republicans would need the support of at least eight Democratic senators in order to reach the 60 votes needed to break a filibuster. And top Democrats are warning that the GOP will get little cooperation from their caucus on a replacement plan if they dismantle the health care law.

"They're going to find repealing Obamacare without putting in a replacement will be far more disastrous and less clever than they think," New York Sen. Chuck Schumer, the incoming Senate Democratic leader, told CNN Thursday. "That's all I'm going to say."

Republicans are gambling that Democrats will buckle, particularly Democratic senators up for reelection in 2018 from states Trump won -- as they face pressure to put a new system in place to avoid chaos in the health care system.

Schumer's chief deputy, Dick Durbin of Illinois, said Republicans have a "responsibility as far as I'm concerned about coming up with a replacement."

Asked if that meant that he'd support Democratic efforts to block a replacement plan, Durbin pushed back.

"Who loses with that approach? If they are successful in repealing it, and we say, 'We're going to stop you in replacing it,'" Durbin said. I want to know what the replacement is going to be. I want to know if it's real protection, and as good as [the Affordable Care Act] for the millions who count on it."

Trump-Hill GOP agenda take shape

In concert with the Trump transition team, GOP leaders are weighing a plan that would delay the health care repeal from taking effect for up to three years, giving Congress time to craft a new system to provide health insurance from the millions who could lose it. They are also planning an ambitious legislative agenda in the new year, moving forward on a plan to rewrite the tax code, a new government funding bill and confirming a spate of Trump's nominees, including to the Supreme Court.

But dealing with the red-hot issue of health care could be the trickiest -- especially since there's no consensus within the GOP yet on what the replacement plan would look like.

Even if the GOP writes into its legislation that a repeal won't take effect for three years, some health policy experts warn that the health care system could collapse immediately because insurers may pull out of the expiring system. That could intensify pressure on the GOP to find a solution right away.

The issue has been discussed at length between House Speaker Paul Ryan, Senate Majority Leader Mitch McConnell and senior Trump officials, sources say. And it dominated talk among top House Republicans in a closed-door meeting Thursday.

Oklahoma GOP Rep. Tom Cole, who attended the meeting, conceded that moving ahead with repeal will put the burden on Republicans to lay out the next steps.

"We do really need to think through how do you do this without kicking a lot of people off of healthcare when they in good faith are responding to the system," Cole told CNN. He noted that his home state, which didn't opt to expand the Medicaid program to provide coverage, won't face the same kinds of challenges that most other states have, where they rely on federal resources for millions who have enrolled in plans.

North Carolina Rep. Mark Meadows, who will chair the conservative House Freedom Caucus next Congress, said the GOP was still sorting out its plans on the issue.

"There's still a lot of discussion about the transition. No one can explain yet what all the details will be," Meadows said Thursday, but said members all agree they want to start with the repeal component early in the new year.

But Cole is confident top GOP leaders working with Rep. Tom Price, R-Georgia, who is Trump's nominee to head the Department of Health and Human Services will methodically manage the process. Moreover, House Republicans on Thursday selected a loyal Ryan ally, Rep. Greg Walden of Oregon, to chair the powerful Energy and Commerce Committee, giving him a key role in drafting a replacement to the health care law.

House Majority Leader Kevin McCarthy told reporters earlier this week that he expected to move legislation to roll back the law first, and hammer out replacement legislation later. But he also believed that once Democrats realized the system they supported was going away, and they would be motivated to be part of the new solution -- or risk appearing too political.

"I don't think you have to wait," McCarthy told reporters.