(AP) —  Joe Biden is taking an aggressive approach to defending the Affordable Care Act, challenging not just President Donald Trump but also some of his rivals for the Democratic presidential nomination who want to replace the current insurance system with a fully government-run model.

Biden on Monday released a plan that would add a “public option” to the 2010 health care overhaul, with expanded coverage paid for by raising taxes on the wealthiest Americans.

He’s repeatedly touted his support for the health care law, often called Obamacare, during recent stops in early voting states. In Iowa, Biden declared himself “against any Republican (and) any Democrat who wants to scrap” the health law. Later in New Hampshire, he said “we should not be scrapping Obamacare, we should be building on it.”

Biden hopes his positioning as Obamacare’s chief defender will be a reminder of his close work alongside former President Barack Obama, who remains popular among Democratic voters. And it could reinforce his pitch as a sensible centrist promising to rise above the strident cacophony of Trump and more liberal Democrats who are single-payer advocates.

The emerging divide between Biden and his progressive rivals could give him an opportunity to go on offense ahead of the next presidential debates at the end of July. Biden has spent the past several weeks on defense, reversing his position on taxpayer funding for abortions and highlighting his past work with segregationist senators. Kamala Harris slammed Biden during the first debates, blasting the segregationist comment and criticizing his opposition to federal busing orders to desegregate public schools during the same era.

Those episodes called Biden’s front-runner status into question, and in New Hampshire over the weekend it was clear he wanted to turn the tables on his rivals backing “Medicare for All.”

“I think one of the most significant things we’ve done in our administration is pass the Affordable Care Act,” Biden said. “I don’t know why we’d get rid of what in fact was working and move to something totally new. And so, there are differences.”

He argued that some of his opponents, with the exception of Bernie Sanders, aren’t fairly representing the consequences of their proposals.

“Bernie’s been very honest about it,” Biden said. “He said you’re going to have to raise taxes on the middle class. He said it’s going to end all private insurance. I mean, he’s been straightforward about it. And he’s making his case.”

Sanders will deliver a health care speech on Wednesday and is already hitting back at Biden. The Vermont senator insists his plan would be a net financial benefit for most households and rejects any suggestion that he hasn’t supported the Affordable Care Act.

“I traveled all over the country to fight the repeal of Obamacare,” Sanders tweeted Monday. “But I will not be deterred from ending the corporate greed that creates dysfunction in our health care system. We must pass Medicare for All.”

Biden’s health care proposal is anchored by a “Medicare-like” plan that any American, including the 150 million-plus Americans now covered by job-based insurance, could buy on ACA exchanges.

The proposal would make existing premium subsidies more generous and expand eligibility for middle-income households, lowering their out-of-pocket costs. It also would extend premium-free coverage to lower-income Americans who have been denied access to Medicaid in Republican-run states that refused to participate in the Affordable Care Act.

The campaign puts the taxpayer cost at $750 billion over 10 years, which would be covered by returning the top marginal income tax to 39.6%, the rate before the 2017 GOP tax cuts . Some multimillionaires also would lose certain capital gains tax advantages.

Biden’s aides framed his plan as more fiscally responsible and politically realistic than a single-payer overhaul. The idea behind a public option is to extend coverage to those who can’t afford decent private coverage, while forcing corporate insurers to compete alongside the government, theoretically pressuring those private firms to lower their premiums and out-of-pocket costs for their policy holders.

The dynamics illustrate Democrats’ overall leftward shift on health care.

A decade ago, the public option was effectively the left-flank for Democrats, a reality made obvious when Obama angered House liberals by jettisoning the provision to mollify some centrist Senate Democrats. Now, after Sanders’ insurgent 2016 presidential bid and his promise of “health care as a human right,” the left has embraced single-payer, with moderates moving to the public option.

Some Democratic White House hopefuls are joining Biden in advocating for the public option, arguing it will be difficult to go much further.

Colorado Sen. Michael Bennet greeted Biden’s proposal with a reminder that he’s been pushing a public option on Capitol Hill. He urged his colleagues Senate colleagues, including Sanders, Harris and Elizabeth Warren, to “reconsider their Medicare for All approach.”

Bennet and Minnesota Sen. Amy Klobuchar are among the moderates arguing that a public option is the next logical move even for single-payer advocates.

“I think it is a beginning and the way you start and the way you move to universal health care,” Klobuchar said in the first debate.

Former Colorado Gov. John Hickenlooper is more frank, warning that Republicans will brand single-payer proposals as “socialism” and reclaim the health care advantage the party enjoyed in the 2018 midterms.