With sweeping economic recovery plans, President Joe Biden seeks his own legacy like the New Deal or Great Society. But he's also bolstering Barack Obama's.

In multiple ways, Biden has used his first 100 days to reinforce the battered foundations of Obamacare. He exercised executive authority to invite more of the uninsured to buy Affordable Care Act coverage, expanded marketing to encourage them and provided larger premium subsidies as part of his $1.9 trillion Covid relief legislation.

More than 500,000 Americans have already taken advantage, according to figures the administration released last week.

With the special enrollment period now extended through August 15, to be followed by normal annual enrollment beginning in November, the number obtaining coverage in ACA marketplaces could soon top its all-time high of 12.7 million during the last year of Obama's presidency.

For its original architects, who spent the last four years watching then-President Donald Trump and fellow Republicans try to wither and wipe out Obama's signature program, it represents a deeply satisfying revival.

"It does need to be shored up and strengthened," observed Nancy-Ann DeParle, a principal health adviser to Obama as the ACA was created. "President Biden and Vice President Harris said they were going to do it, and they're doing it."

For obvious reasons, Biden holds a strong stake in the program's success. As vice president, he too was present at the program's creation, famously whispering in Obama's ear that fulfilling the Democratic Party's decades-old wish for a national health plan represented a "big f------ deal."

In the 2020 campaign, Biden resisted calls from primary rivals and the Democratic left to embrace a "Medicare for All" single-payer system to replace the ACA. But his health care agenda extended beyond simply reinforcing Obama's existing structure.

He proposed to make Medicare available to a large new swath of Americans by dropping the age of eligibility to 60 from 65. And he called for a new Medicare-style "public option," available even to those offered health insurance coverage by their employers.

Both those proposals face stiff political headwinds in Congress, especially with the White House making massive economic recovery spending on physical infrastructure and other priorities the focus of its current legislative push. Meanwhile, Biden used the Covid relief bill to make a big health-policy down payment.

The steps it included could help extend coverage to more than one-third of the 29 million Americans currently without health insurance, according to Larry Levitt of the Kaiser Family Foundation. In addition to expanding the breadth and depth of subsidies for the purchase of Obamacare policies, the Covid relief bill extended huge new financial incentives for states to expand their Medicaid programs under provisions of the ACA.

Expansion under Obamacare extends Medicaid coverage to those with incomes below 138% of the federal poverty level. Twelve states -- 10 of which Trump carried in both his presidential campaigns -- have resisted doing so since the ACA was enacted in 2010.

If all 12 accepted Biden's new incentives to expand, roughly 4 million people could gain insurance under Medicaid. None has accepted so far. In Missouri, the Republican-controlled legislature is blocking implementation of Medicaid expansion even after state voters passed a ballot measure expanding Medicaid last year.

But Biden and his outside allies haven't given up. The liberal advocacy group Protect Our Care has launched a public campaign to pressure "GOP Medicaid Deniers," while health policy experts close to the administration explore alternatives if the holdouts persist.

"We've got to find a way to get this group covered," said Sharon Parrott, president of the Center on Budget and Policy Priorities.

And DeParle predicted the Biden administration "will be very creative" about overcoming lingering resistance.

Later this month, the second part of Biden's economic recovery agenda -- an "American Families Plan" to help struggling families climb the economic ladder -- may sketch out an approach. One possibility under discussion: a limited-purpose public insurance option for those stuck in the holdout states' "Medicaid coverage gap."

The expanded premium subsidies in the Covid relief bill last only two years. The White House wants to make them permanent, but that requires additional legislation.

Nor has Biden yet eliminated an existential legal threat to Obamacare. The Supreme Court, reshaped by three Trump-appointed justices, has not yet ruled on a lawsuit by Republican-led states that seeks to declare the ACA unconstitutional.

But many legal experts expect the court to once again uphold the law. Chief Justice John Roberts and Trump appointee Brett Kavanaugh suggested as much during oral arguments last November.

Public support for the law has actually risen during its extended legal and political trial by fire. After Trump and the Republican-led Congress nearly repealed it in 2017, voters handed Democrats the House in 2018 and then full control of Congress and the White House in 2020.

Under Biden's protection now, Obama's legacy achievement appears likely to remain a durable feature of the American landscape. Invoking an earlier generation's television commercial for a watch, DeParle concluded: "Takes a lickin' and keeps on tickin'."