Joe Biden thinks the prescription to fix the current healthcare system is doubling current doses, not drastic surgery.

The former vice president laid out his plan to expand rather than replace Obamacare Monday morning, taking aim at the more far-reaching Medicare-for-All plan advocated by his 2020 opponents as he dug in on one of the defining policy disagreements of the 2020 Democratic primary.

The core of Biden’s plan is a proposal to create a government-run insurance policy as an option for people to choose over private insurance. That’s something most Democrats wanted to do when passing Obamacare in the first place, but failed to pass. The former vice president’s plan would also allow Medicare to directly negotiate prescription prices and allow drugs to be imported from abroad, both of which would drive down drug costs, as well as beef up tax credits to help poorer people afford insurance. The plan would cost approximately $750 billion, according to Biden’s advisers — a cost that would be paid for by rolling back some of President Trump’s tax cuts.

But what the plan doesn’t contain is as important as what it does for the purposes of Democratic primary politics. Biden takes sharp aim at Medicare for All, a plan championed by Sen. Bernie Sanders and backed to varying degrees by Biden’s two other chief primary opponents at this point, Kamala Harris and Elizabeth Warren. Their proposal would move everyone into government-run insurance and end most types of private insurance policies.

The fight between Biden and his more left-wing opponents isn’t just about policy. It’s also a deeper if more nebulous disagreement: Do Democrats looking for someone who can return the party to the Obama era, or do they want a more aggressively liberal candidate as their standard-bearer? The answer could define the primary and determine whether Biden wins the nomination.

“The question was asked, whether we support eliminating private health insurance. Some said yes, I said absolutely not. I believe we have to protect and build on Obamacare. That’s why I proposed adding the public option to Obamacare as the best way to lower cost and cover everything. I understand the appeal of Medicare for All but folks supporting it should be clear that it means getting rid of Obamacare, and I’m not for that,” Biden said in a video announcing the plan.

Biden, who worked with President Obama to pass the president’s signature policy achievement, then compares those on the left looking to start from scratch to the Republicans who’ve spent most of the last decade trying to end Obamacare.

“Starting over makes no sense to me at all. I knew the Republicans would do everything in their power to repeal Obamacare - they still are. But I’m surprised that so many Democrats are running on getting rid of it,” he said.

The disagreement over Medicare for All is the clearest dispute within the Democratic primary, and Biden allies see an advantage to be won. Polls show “Medicare for All” as a general term remains popular — but that it’s deeply misunderstood, as majorities of people assume that it means they’d have the option to buy into a government-run health insurance plan rather than be forced onto one. Other polling indicates that most Americans don’t support a plan that would eliminate private insurance — a January survey from the Kaiser Health Foundation found support for Medicare for All dropped from 56% to 37% when people were told it would eliminate private insurance.

Sanders sees this issue as a defining one as well — he plans to make a major speech defending his plan on Wednesday in Washington. Harris and Warren, meanwhile, have been caught in the middle. Both are cosponsors of Sanders' plan. Warren has been more assertive in her support, while Harris has repeatedly tried to dance around whether she fully supports Sanders' proposal.