(CNN) Republicans have spent years bashing Obamacare. Now, they're about to own it.

When Congress returns to Washington on Tuesday, the Republican Party -- which controls the House and the Senate and will soon see GOP President-elect Donald Trump sworn into office -- will move quickly to repeal President Barack Obama's landmark healthcare law.

These first steps to unravel the Affordable Care Act have been years in the making, and will mark a symbolic victory for the conservative movement.

Since Obama's 2008 election, no other single political and policy issue has been more effective in uniting the GOP in opposition and electrifying the party's base. The massive healthcare reform has fueled Republican rallying cries and partisan campaign messaging in every election since it became law in 2010.

"People must remember that ObamaCare just doesn't work, and it is not affordable," Trump tweeted Tuesday morning, adding that the law is "lousy."

People must remember that ObamaCare just doesn't work, and it is not affordable - 116% increases (Arizona). Bill Clinton called it "CRAZY"

But repealing Obamacare won't be a clean political win for Republicans.

In fact, dismantling the law will leave the GOP with a complicated political and policy conundrum: Even if Republican lawmakers delay the repeal from going effect for some years, as they are currently discussing, the initial vote will trigger a years-long, contentious fight over how to replace the law, and unleash widespread uncertainty for patients and the insurance market.

In other words, Republicans could suddenly find themselves fielding the very kind of criticism and blame that they've been throwing at Democrats for years -- that of having created an untenable and unpopular healthcare system. And the question over how to fill the new gaps in healthcare coverage will expose ideological divisions among conservatives.

"For Republicans, the challenge is following through on the promise not just to repeal the law -- because in some ways that's easy -- but to replace it," said Lanhee Chen, Mitt Romney's former chief policy adviser.

Here's how we got to this moment, and why the stakes are enormous for Republicans:

Obamacare: Partisan from the very beginning

When Obama took office in January 2009, the country was spiraling into a deep recession and the new president's most urgent order of business was to stabilize the economy.

But even amid the economic chaos, Obama moved full steam ahead with his top personal priority: reforming the country's healthcare system.

His insistence on using his party's control at the time of both chambers of Congress to make sweeping healthcare reforms -- a goal that had eluded his Democratic predecessors -- would spark one of the most acrimonious political fights in Washington seen in modern history.

Republicans warned that what Obama and his fellow Democrats were proposing would amount to a "government takeover" of the healthcare system. One of the most notorious and misleading phrases to emerge was "death panels" -- coined by former GOP vice presidential nominee Sarah Palin -- which stoked fears that the ACA would decide which Americans were worthy of receiving health coverage.

After more than a year of bitter partisan debate, the House passed the bill in a 219-212 vote and sent it to Obama. All House Republicans voted in opposition.

Then-GOP House Minority Leader John Boehner signaled his party's severe hostility towards the ACA when he lamented at the time: "Look at how this bill was written. Can you say it was done openly? With transparency and accountability? Without backroom deals that were struck behind closed doors? ... Hell no, you can't!"

A haunting vote for Democrats

Democrats would quickly suffer the painful consequence of Obamacare at the ballot box.

Seven months after Obama signed the Affordable Care Act into law, the Democratic Party saw huge losses during the midterm elections. Running against the controversial reform, Republicans decisively took back control of the House and gained seats in the Senate.

The election was an agonizing reality check for Democratic lawmakers -- particularly moderates and those in conservative areas -- who had expressed reservations about the controversial law.

Former Democratic Rep. Bill Owens of New York, who was narrowly reelected in 2010, said Obamacare was one of the most contentious issues in all three of his congressional elections.

"What the Republicans were able to do was gin up emotions about it," Owens told CNN. "And they did that very successfully, there's no doubt about it."

Owens reflected that in retrospect, Democrats fundamentally mishandled the politics of the ACA. A major misstep, he said, was a failure to explain the realities of the new law to the American public as it struggled to understand how it would directly impact their coverage.

"There was a failure to communicate the benefit that was being derived by large numbers of people," Obama said. "Democrats didn't do a good job of saying, 'We are getting people to a doctor.' And it was hard to explain that this was going to take some years before it starts to reduce the costs associated with healthcare. That's a very hard explanation."

Early setbacks

As Republicans continued to savage the law, the ACA suffered early setbacks.

The law faced an onslaught of legal challenges, and in the summer of 2011, a federal appeals court ruled key provisions of Obamacare unconstitutional. In 2012, the Supreme Court upheld the individual mandate , but made Medicaid expansion optional.

Meanwhile, Obama's famous pledge -- that "if you like your plan, you can keep your plan" -- became a lightening rod for critics of the law, as some Americans received cancellation notices from their insurance companies and found that they couldn't keep their plans.

And in a major PR disaster, the Healthcare.gov website was hit with serious glitches in the fall of 2013, just as Republicans were paying a political price for shutting down the government over Obamacare. The portal crashed more than once, and along with many of the state exchanges, was largely unusable for weeks, leaving hundreds of thousands of people struggling to sign up for coverage. The fiasco only fueled GOP fury, and led to then-secretary of Health and Human Services, Kathleen Sebelius, to resign months later.

Tevi Troy, the deputy secretary of Health and Human Services under President George W. Bush, said these mistakes helped ensure that Obamacare would remain a powerful weapon for Republicans.

"They've run against it for so many cycles in large part because it's not popular and it's also not working the way it was touted to be working," Troy said.

Dems to GOP: If you break it, you own it

Repealing Obamacare comes with a whole lot of baggage.

In fact, the GOP is about to be consumed by the hugely complex burden of replacing what they repeal.

An estimated 20 million people obtained health coverage through the individual exchanges and Medicaid expansion, and Obamacare made major changes to the healthcare system, like preventing insurance companies from denying coverage to those with pre-existing conditions.

"Democrats have not enjoyed owning what they've been calling a crap sandwich for the last six years. That's not a fun thing to own," Troy said. "They want to give that to Republicans as quickly as possible."

As soon as Congress comes back to town on Tuesday, Republicans intend to act swiftly to begin the process of repealing the ACA through a fast-track budget reconciliation bill, but it could be days before the vote actually take place.

But there's a catch: Republicans don't yet have a replacement plan. This is why GOP leaders are discussing a "replace and delay" option, which would keep the repeal from going into effect for a few years and buy time to figure out what's next.

Already, the potential uncertainty is creating jitters among insurance companies, and experts warn that if insurers pull out of the marketplace, premiums could spike and millions are at risk of losing coverage.

House Minority Leader Nancy Pelosi said Republicans are eager to repeal the law but don't know what to do next.

"They have shown nothing in their ranting and raving that shows any level of knowledge of where they would go or where they would take this," Pelosi told reporters Monday, describing the GOP strategy of "repeal and delay" as "an act of cowardice."

Chen, the former Romney adviser, said it would be a "mistake" for the GOP to repeal Obamacare if there is no plan to replace it quickly.

Republicans will have trouble getting help from Democrats on replacing major portion of the ACA -- a political reality that could also haunt the party in the next midterms.

"Politically, I think Democrats are going to start to drag their heels on this," Chen said. "So (Republicans) have to be wary of the fact that Democrats see some political opportunity here, potentially."

The Obama legacy

Obama is making a rare visit to Capitol Hill on Wednesday.

His mission: huddle with Democrats to discuss how the party can try to preserve his signature healthcare reform law.

The President is also expected to discuss the healthcare law in a "farewell" address in Chicago next week, aimed at touting his key accomplishments over the last eight years.

The reality, of course, is that there's little that the President can do once he's out of office, and when it comes to Obamacare, Republicans have been emphatic about their intention to dismantle the law.

To rally Republicans, Vice President-elect Mike Pence is also visiting the Hill Wednesday.

How far Republicans can go in changing the fundamentals of the Affordable Care Act will determine Obamacare's place in the president's future legacy.

GOP lawmakers have acknowledged concerns about messing with some of the law's most popular provisions, such as the pre-existing condition provision and the ability for parents to keep children on their plans until they are 26.

"Ultimately, some form of Obamacare will be in existence 10 years from now," said Owens, the former Democratic congressman. "They will wind up making changes to it -- and they may even call it something else. But the depths of the law will probably stand for a very long time."