Sen. Cory Booker has revived the debate over whether the existence of the filibuster actually prevented Obamacare from being repealed in 2017.

As liberals push Democrats to rally around a sweeping policy agenda, they are also confronting the reality that as long as there is a 60-vote threshold for passing legislation in the U.S. Senate, their transformational ideas such as socializing the health insurance system and imposing the Green New Deal will never become reality.

That's why, in addition to pushing Democratic candidates to get behind radical policy ideas, activists are also pressing presidential contenders to embrace an effort to end the filibuster, which would allow the Senate to pass bills with a simple majority. Though it seems as though this would be a no-brainer for Democratic candidates seeking to pander to an energetic base, in a field dominated by senators, policy radicalism has been met repeatedly by procedural timidity when it comes to questions about eliminating the filibuster. Even Sen. Bernie Sanders, I-Vt., no stranger to staking out extreme positions, has said, "I'm not crazy about getting rid of the filibuster."

Recently, Booker has been testing out an argument with liberal audiences in which he acknowledges the concerns about the 60-vote threshold while warning about what Republicans could have done were they unrestrained by the filibuster. He made the case last month on the popular "Pod Save America" show. And he did it again on Monday in response to an audience question following a speech at the We the People conference.

“Some people are saying ‘Let’s get rid of the filibuster,’ and I feel that same sense of urgency," Booker said. "But let me tell you what I worry about. In my community, if Mitch McConnell, Paul Ryan, and Donald Trump had two years like they just had without me in the Senate and other noble progressives who fought them with you to prevent the taking away of healthcare, we would have lost that battle — Obamacare would have been gone.”

The idea that the filibuster prevented Republicans from being able to repeal Obamacare is a popular one pushed by both Republicans trying to explain away their failure to deliver on a campaign promise dating back to 2010, and Democrats such as Booker trying to wave away demands for killing the filibuster. But is it an accurate account of what actually happened?

The truth is a bit more complicated than it's made out to be by proponents of this idea on both sides.

In the most straightforward answer is, no, the filibuster did not technically stop Republicans, because they were unable to obtain 50 votes for any plan to repeal any part of Obamacare, with Vice President Mike Pence ready and willing to provide the tie-breaking vote on anything they could pass.

The counter to this overly simplified way of looking at things is that the threat of the filibuster forced Republicans to seek to pass legislation through the alternate legislative maneuver known as reconciliation, a process that, while enabling a ruling party to pass legislation with a simple majority, imposes restrictions on what can be in any such bill. It has been argued that the reconciliation rules prevented the normal horse-trading that goes on in making policy on Capitol Hill, crippling negotiations by limiting McConnell's ability to offer the necessary concessions to get fence-sitting senators to "yes."

That having been said, there is also a counter to this. Though reconciliation created an obstacle for McConnell, it also worked to his benefit in another sense by serving as a handy excuse that allowed him to cut off demands. Conservatives, for instance, wanted to strip out Obamacare regulations that were driving up premiums, but doing that would lose centrists worried that going after regulations would undermine coverage for those with pre-existing conditions. McConnell was able to tell these conservatives, essentially, "Hey, I'd love to get rid of the regulations, but my hands are tied by reconciliation rules." By the end of the process, conservatives on the Hill had become exasperated by how often the Senate parliamentarian was used as a reason why a certain conservative reform could not be adopted. Had there been no filibuster, McConnell would not have such an excuse, so he would have been under more pressure to accommodate conservatives in ways that would have risked losing centrists.

I've gone back and forth on this, but at the end of the day, I'm not convinced Republicans would have been able to pass something in the absence of a filibuster. The core problem was that for years, Republicans did not lay the groundwork for an Obamacare alternative. They came into office with a razor-thin majority and very real differences on healthcare policy. On the one hand, you had conservatives who were eager to repeal all of Obamacare and push for real free market reforms, and on the other hand, you had centrists that ultimately wanted to preserve much of Obamacare. After all, in 2015, Republicans passed a bill to repeal much of Obamacare, and six senators who voted for that bill, voted "no" two years later on the identical bill, the only difference being that in 2017 the bill would have actually become law. Given the reticence of a core group of senators on one side to vote for any significant repeal, and conservatives on the other side that wanted to hold Republican leadership to their campaign promises, it's hard to see the outcome ending differently, with or without the filibuster. When it came to passing a large tax cut, Republicans found a way to get it done because cutting taxes was ultimately unifying to the party. Healthcare was not.