Senate Republicans’ latest effort to repeal the Affordable Care Act has collapsed, but President Trump has already made moves to undermine important provisions of the health law, and there is still more he could do.

What Trump can do Status Weaken enforcement of the individual mandate. In progress Impose work requirements for Medicaid recipients. In progress Fail to do advertising or outreach. In progress Make tax credits for premiums less generous. In progress Defund subsidies that help people pay out-of-pocket costs. A possibility Redefine essential health benefits. A possibility

In progress

1. Weaken enforcement of the individual mandate.

How this would hurt Obamacare: Fewer healthy people may sign up for insurance, driving up prices for those who need it most, like older people and the sick.

The Affordable Care Act requires all Americans to buy health insurance or pay a penalty, with exceptions for people with hardships.

While Mr. Trump cannot eliminate the mandate, as Republicans in Congress sought to do, the Internal Revenue Service has said it will continue accepting tax returns that do not say whether a filer has been uninsured, weakening its enforcement of the provision.

The administration could also allow for more exceptions, making it easier to avoid the tax penalty. It could instruct the I.R.S. to scrutinize people’s returns less closely. And it could signal publicly that it does not care about the mandate, which may cause people to be less likely to sign up, even if they later get hit with a tax penalty.

In progress

2. Impose work requirements for Medicaid recipients.

How this would hurt Obamacare: Many people who gained coverage through Medicaid expansion may not be able to afford insurance or participate in the program.

Under the Affordable Care Act, 31 states expanded Medicaid coverage to poor adults who were previously uncovered. And Republicans in Congress sought to sharply curtail federal support for the expansion, likely causing many states to end it.

Mr. Trump cannot unilaterally prevent states from expanding Medicaid in the future. He could, however, allow states that apply to impose work requirements or charge premiums for more Medicaid beneficiaries, through a process that lets the government waive the normal Medicaid rules. Those changes might make it difficult for as many poor Americans to access the system.

In March, the Health and Human Services Department said it would be open to states’ proposing work requirements for Medicaid recipients.

In progress

3. Fail to do advertising or outreach.

How this would hurt Obamacare: Without outreach, the number of Americans who learn about the Affordable Care Act and sign up for coverage could dwindle.

The Trump administration said in August that it would slash spending on advertising and promotion for enrollment to $10 million from $100 million. It also said it would cut funding, by about 40 percent, to groups that help people enroll.

The Department of Health and Human Services, which is in charge of administering the health law, has also been waging a multipronged media campaign to undermine it, using videos, Twitter posts and the agency’s website.

The last sign-up period for the Affordable Care Act ended 11 days after Mr. Trump was inaugurated. During the those final days of enrollment, the Trump administration pulled advertisements and outreach off the air that encouraged people to sign up for health insurance under the law.

In the last few years, large number of consumers generally signed up just before the deadline, and sign-ups for health plans in states managed by the federal government were down slightly compared to the same period the previous year. Lower signups tend to mean higher prices, since the sickest customers are more likely to investigate their insurance options, regardless of government outreach.

In progress

4. Make tax credits for premiums less generous.

How this would hurt Obamacare: Many customers may end up with plans with higher deductibles and co-payments.

The Affordable Care Act gives tax credits to middle-income Americans to offset the cost of premiums. Those subsidies are based on a particular plan, meant to cover 70 percent of the average customer’s medical bills.

The administration put in place a new rule that in 2018 will make the credits apply to a slightly less generous plan for all Obamacare customers. The size of the changes will be much smaller than reductions that had been proposed in the Republican health care bills. But many customers will end up with either more expensive insurance or plans that have higher deductibles and co-payments in 2018.

A possibility

5. Defund subsidies that help people pay out-of-pocket costs.

How this would hurt Obamacare: Insurance companies would take a big financial hit, since they assumed they would get the subsidies when pricing their plans.

Obamacare provides subsidies to help insurance companies reduce out-of-pocket costs, like deductibles and co-payments, for lower-income customers. Insurance companies price their plans assuming payments will be based on how many eligible customers they serve. The House and Senate health bills would have eliminated the subsidies, allowing insurers to charge those customers higher deductibles.

Mr. Trump could effectively defund the subsidies if he stops the appeal of a lawsuit that was started under the Obama administration. President Barack Obama’s lawyers had appealed a court ruling that said the subsidy payments were made without proper congressional authority.

Removing the subsidies this year would cause insurers to lose money right away, and it could create substantial financial distress for smaller insurers. On Wednesday, insurers must sign final contracts for 2018 policies. Because of the uncertainty, many have increased their prices and some have decided to exit the market, reducing consumer choices.

The White House has declined to say whether it will continue to pay the subsidies.

A possibility

6. Redefine essential health benefits.

How this would hurt Obamacare: Customers with health problems may end up with really high insurance costs.

Under the current law, all insurers must offer 10 categories of essential health benefits, like maternity treatment and hospital care. Conservatives considered the requirements too restrictive.

Congress tried to loosen these rules by letting states apply to waive them. Republicans in the Senate also tried to let insurers get away with offering plans that don’t meet the rules as long as they offered ones that did.

Mr. Trump cannot eliminate the 10 broad categories of benefits, but his administration has some discretion on how the categories are defined.