The Affordable Care Act is still, as House Speaker Paul Ryan put it, "the law of the land." So now the Trump administration faces a hugely consequential decision: How much should it do to make Obamacare work?

The executive branch cannot repeal the Affordable Care Act on its own. Still, it has huge sway over how well (or poorly) the insurance marketplaces that cover 12 million people will function this year.

"They have a lot of discretion," says Michael Adelberg, who ran the Center for Consumer Information and Insurance Oversight under President Obama.

Obamacare's collapse is now, in fact, part of President Trump's repeal-and-replace strategy. “The best thing we can do, politically speaking, is let Obamacare explode," Trump said Friday after the House canceled its vote on the replacement plan. Obamacare collapsing, Trump's argument goes, will create a window for Republicans to move forward on putting a new plan in place.

Keep that context in mind when you consider the decisions the Trump administration will need to make in coming weeks and months. They include choices like:

Should it run an aggressive outreach campaign encouraging uninsured Americans to buy coverage — or should it continue with minimal advertising, which could depress enrollment and drive up premiums?

How should it handle " empty shelf " counties, where no insurance plan wants to sell coverage on the marketplace? The Obama administration used to work overtime to ensure that at least one insurer signed up to sell coverage. Will the Trump administration do the same, or will it sit back and leave parts of the country with no insurance options at all?

" counties, where no insurance plan wants to sell coverage on the marketplace? The Obama administration used to work overtime to ensure that at least one insurer signed up to sell coverage. Will the Trump administration do the same, or will it sit back and leave parts of the country with no insurance options at all? Will it continue to pay for the cost-sharing reduction subsidies that make marketplace coverage affordable for the lowest-income ACA enrollees? House Republicans have a pending lawsuit arguing that those subsidies are illegal — that Obamacare didn't actually appropriate money for this part of the law. The Obama administration was fighting that lawsuit. Will the Trump administration do the same?

These decisions will have big consequences. Deciding not to run a big outreach campaign, for example, would near certainly reduce Obamacare enrollment.

We know that because of recent work from the University of Minnesota's Pinar Karaca-Mandic and Sarah Gollust, who worked with the Wesleyan Media Center to look at the relationship between Obamacare television ads and enrollment.

The number of ads varied a lot from county to county, so the researchers could look at what was different about the places that had lots of Obamacare television spots.

Karaca-Mandic and Gollust found that an additional 1,000 ads was associated with a 0.1 percentage point decline in the uninsured rate.

"What's critical now for the sustainability of the marketplaces is that people with fewer health needs need to continue to enroll," Gollust says. "Any changes to reduce the penalties or stop marketing would have a large and destabilizing impact."

Obamacare's marketplaces aren't imploding. But if Trump wants them to, they could. The Obama administration really, really wanted the marketplaces to run smoothly. Under President Obama, the agencies implementing the law were staffed with people who cared deeply about the health care law and its success.

A commitment to success could only get the Obama administration so far. The marketplaces today are functional; they are not, as some conservatives argue, in a death spiral. But they are not the robust, competitive marketplaces that Obamacare's drafters wanted either. One-third of the counties on Healthcare.gov had just one insurer offering coverage in the last open enrollment. There are currently 16 counties in Tennessee without any insurer signed up to sell.

"For the sake argument, let’s say ACA market is functioning at a C- today,” Adelberg says. “It is possible for the Administration to get it working better, maybe up to a B-. But that might require making some hard decisions that will be questioned by some within the caucus."

If the Obamacare marketplace is going to work next year, the Trump administration will need to actively work to make that happen. It will have to decide whether to play a role in saving the law — whether, for example, to try to cajole an insurer into selling coverage in those 16 Tennessee counties. The Trump administration will have to decide to buy airtime to advertise the benefits of signing up for coverage.

Will a president who campaigned on Obamacare repeal — and who has predicted the law's implosion — be willing to take those kinds of active steps to make the law work better?

We're about to find out.

Chart of the Day

This chart shows the huge variation in how many Obamacare ads states saw during the first open enrollment period. It comes from the research discussed earlier, from the University of Minnesota's Pinar Karaca-Mandic and Sarah Gollust.

Kliff’s Notes

With research help from Caitlin Davis