President Barack Obama is campaigning for Hillary Clinton so fervently these days you might think he is on the ballot, too.

That’s because he is.

No, Obama can’t stay in office past Jan. 20. But the difference between electing Clinton and Donald Trump isn’t simply about new policies the candidates would advocate. For the president and his longtime aides ― many of whom have been impassioned Clinton advocates in this election cycle ― it’s also about making sure Obama’s legacy, and progressivism as a whole, is firmly ingrained in American society.

“We know how important and impactful having the White House is, and Clinton winning would cement many of President Obama’s biggest accomplishments,” said Dan Pfeiffer, Obama’s longtime communications hand. “Winning three elections in a row can shift the tectonic plates of the political debate towards the left. Just look at how Reagan and his philosophy came to dominate politics for decades. That doesn’t happen if [Michael] Dukakis wins in ‘88.”

Obama has made this clear on the stump ― like he did the other day in Cleveland, when he talked about some of his accomplishments and warned supporters that “all that progress goes out the window if we don’t make the right choice, right now.”

His aides say the same thing. And, in conversations with The Huffington Post, they make explicit a point that Obama often implies: That adding four more years of a Democratic presidency to Obama’s eight years in office would fundamentally change public expectations about what government can or should do, while setting in motion legal and regulatory changes that successors would find almost impossible to undo.

“What it does is, at the end of her term or two terms ― even if it is one term ― you can’t have the gutting of that legacy,” said Bill Daley, Obama’s former chief of staff. “I don’t know if this election is the exclamation point, because there are going to be changes. But whatever changes she makes will be more productive. Whereas, I think there has been a very strong sense that if the Republicans got the presidency back right after his term, you could undo a lot.”

From workplace standards to environmental regulations, many of Obama’s accomplishments have taken firm root. But they’d become seemingly unshakeable after four more years.

Here are some of those advances spotlighted in conversations with both Obama and Clinton aides and advisers.

Andrew Harnik/ASSOCIATED PRESS

Health Care

The Affordable Care Act remains a work in progress, with rising premiums and the withdraw of insurers causing serious problems in some parts of the country. But more than 20 million people now get insurance through the Obamacare exchanges. And many millions more have come to expect that the law’s consumer protections ― like guaranteed coverage for pre-existing conditions ― are how health insurance is supposed to work.

The 2016 election probably represents the last shot Republicans have to completely repeal the law and replace it with something different. (And even that’s a long shot.) After Obama, Republicans still might be able to make modifications, maybe even substantially, by reducing funding and relaxing regulations on insurance.

But it’s difficult to imagine the GOP ripping out the wiring of Obamacare altogether, given the disruption it would cause. And that goes double for the law’s “payment reforms” ― that is, changes in the way Medicare pays for care, in order to hold down costs and improve quality.

Climate

Obama failed at his one, highly visible attempt at passing climate legislation ― an effort to create a cap-and-trade system to reduce carbon emissions. Nevertheless, he used wide-ranging authority under the Clean Air Act to limit production of greenhouse gases. Early in his presidency, he issued new regulations requiring the auto industry to produce vehicles that get better mileage and emit less pollution. More recently, he issued rules forcing utilities to reduce emissions from power plants ― a mandate that will force companies to dial back reliance on coal while increasing use of renewables.

The power plant rules would not survive long under a Trump presidency. Either he’d rescind them on his own, or Congress would pass a bill undoing them and Trump would sign it. A Clinton victory would leave the rules in place. And assuming they survive a court challenge, as seems likely, it’s only a matter of time before state officials and utility companies make plans to abide by the new standards ― at which point, there’s basically no turning back.

It worked out that way with the regulations on motor vehicles. They were controversial, but the industry adapted. Just this summer, federal regulators issued a report congratulating the auto industry, because companies were actually ahead of schedule on meeting new emissions goals.

Oh, and Trump as president would also probably try to pull out of the 2015 Paris climate agreement, the first worldwide deal to limit greenhouse gases. He’d also likely do the same with a bilateral agreement that Obama reached with China, setting emissions reductions for each country. Both agreements were pledges without the force of treaties, because Obama couldn’t get assent from the Republican-led Congress. Clinton has praised these deals and would stand by them. And, four years from now, it would be difficult for even a hostile U.S. president to pull out of them ― at least without severe diplomatic repercussions.

Workplace, Labor Regulations

This is another set of issues in which Obama, faced with an intractable Congress, acted alone. In his second term, he issued regulations to provide higher pay and benefits to federal employees (giving them paid sick days) and contractors who provide services to the federal government (also giving them paid sick days, plus a higher minimum wage).

But one key change affected people who aren’t part of the workforce. Obama issued a regulation changing the rules for overtime pay, so that anybody making less than $47,476 a year is eligible for overtime ― even if he or she is a salaried, rather than hourly, employee. Previously, the threshold was $23,600.

That regulation takes effect in December, which means it will be brand new in January, when the next president takes over. A hypothetical Trump administration could rescind it, weaken it, or fail to enforce it ― thereby making it vulnerable to erosion later on.

Clinton, by contrast, has pledged to enforce these kinds of rules. And once these workplace regulations have been in place for a few years, it’d be difficult, if not impossible, to rescind them. A high political cost comes with trying to take pay or benefits away from people used to getting them.

The same likely goes for rules that the Obama administration issued for the management of retirement savings accounts ― effectively forcing managers to put interests of clients ahead of their own profits. Like the overtime rules, they are new and controversial. Trump could easily rescind them. They could also fall victim to legal challenges. By contrast, Clinton would keep them in place and, in the process, make it unlikely a future president or Congress would rescind them, at least openly. The financial industry, after all, is already creating new products to abide by the rules.

Immigration

Although unable to win comprehensive immigration reform, the Obama administration issued a series of orders that set new priorities for immigration enforcement ― and, perhaps more importantly, gave a reprieve to certain categories of undocumented immigrants. In particular, Obama issued Deferred Action for Childhood Arrivals, or DACA, which has meant temporary work permits and driver’s licenses ― and no active threat of deportation ― for hundreds of thousands of undocumented residents who arrived in the U.S. as children.

Stopping illegal immigration and deporting undocumented workers already in the U.S. have been the Trump campaign’s central promises. While Trump has sent mixed signals about his commitment to mass deportations, he seems likely to make at least some effort to take away the protections DACA recipients now have.

Clinton, on the other hand, has vowed to expand DACA. And while such efforts could face judicial scrutiny, just as Obama’s have, it’s safe to assume that her election would leave DACA participants able to work (and pay taxes) while remaining with families in the U.S. ― not just for the short term, but for the long term as well.

Foreign Policy

Though it seems unlikely that Clinton, given her history, will strictly adhere to the cautious realism that has defined the Obama years, there are critical policies that she would cement and that Trump would threaten. The thawing of the U.S. relationship with Cuba is almost certain to continue under a Clinton administration, as is the implementation of the Iran nuclear deal, which she helped initiate when she was at the State Department.

“The deal is fragile. I think lots of people would say that. And in some ways that is independent of intentions if you think the deal is good. But if you want to break it down, the deal would be in dire straights if Trump were to win,” said Joseph Cirincione, president of Ploughshares Fund, an anti-proliferation group and a big booster of the Iran pact. “Hillary has been quite clear, as have her advisers, several of whom helped negotiate the deal, that this is a good deal and in the United States’ national security interest.”

Mark Duncan/ASSOCIATED PRESS They battled each other in 2008. Now, they need each other in 2016, albeit for different reasons.

For Clinton’s campaign, the argument that her election would serve as a solidifying point for the accomplishments of the Obama years is not without complications. There are elements of Obama’s agenda that remain unpopular. But a larger concern for aides is that she must make the affirmative case for her own candidacy, and not be seen solely as an agent of the status quo.

Still, in recent weeks, Clinton’s campaign has begun embracing the idea that Nov. 8 could be a rubicon-crossing moment for progressive governance. Her campaign recently put out an ad, narrated by Morgan Freeman, that made the pitch that her election would be an act of political continuity with Obama.

“What does showing up when it’s time to vote actually mean? You care about protecting his legacy and our progress,” Freeman says.

In addition, the Clinton campaign has been sending out brochures in to African American communities making the case that Trump’s modus operandi is to undo the past eight years.

Clinton Campaign

All this would have seemed unthinkable just two years ago, when Senate Democrats were petrified to appear alongside Obama, let alone tout his (and their) agenda. But as the president’s popularity has risen, that calculus has changed. And as Election Day approaches, the party is now openly embracing the concept that four more years of White House control can fully immunize the last eight years of achievement.

“Hillary Clinton is running for her first term, not anyone else’s third term,” her spokesman, Brian Fallon, said in a statement. “But there is no question that as president, she would seek to build on all the progress we have made under President Obama.”

Dave Jamieson and Elise Foley contributed reporting.