House Republicans left for spring break last week, without reaching a deal to repeal and replace the Affordable Care Act. Their bill to overhaul the health care system collapsed on the House floor last month, amid divisions in the caucus.

Even without Congress, however, President Trump has the authority to modify important provisions of the health law, including many that House Republicans sought to change or repeal. Here are some examples of actions he could take (or has already taken):

Individual mandate

What the bill tried to do Eliminate the mandate What Trump is doing Weakening enforcement

The Affordable Care Act requires all Americans to buy health insurance or pay a tax penalty. There are exceptions for people who have experienced hardships.

While Mr. Trump cannot eliminate the mandate as the Republican bill would have done, 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.

Subsidies for deductibles and co-payments

What the bill tried to do Eliminate subsidy What Trump can do Eliminate subsidy

Obamacare provides subsidies to help people with lower incomes pay for out-of-pocket costs like deductibles and co-payments. The Republican bill would have eliminated these subsidies in 2020.

Mr. Trump could effectively achieve the same thing 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 that the subsidy payments were made without proper congressional authority.

Ending the subsidies is one of the most immediate things Mr. Trump could do to undermine the Affordable Care Act's marketplaces, said Larry Levitt, a vice president at Kaiser Family Foundation. Without the payments, insurance companies will lose money and some may go bankrupt. Many would exit the markets.

A spokeswoman for the Department of Health and Human Services said Tuesday that “no decisions have been made about how the administration will proceed.”

Tax credits for premiums

What the bill tried to do Change the whole subsidy structure What Trump can do Make subsidies less generous

The Affordable Care Act gives tax credits to middle-income Americans to offset the cost of premiums.

The Republican bill would have reduced that help for some people, like older Americans with low incomes. But it would also have been more generous to some Americans with higher incomes.

Mr. Trump has proposed a regulation that would make the credits slightly less generous for all groups, not just those that would have been hurt by the Republican bill. The size of the changes is much smaller, but still means that many customers will end up with plans that have higher deductibles and co-payments.

Medicaid expansion

What the bill tried to do Cut funding What Trump can do Impose work requirements

The Republican bill would have cut the amount of money the federal government gives to states to help care for people who got Medicaid.

And an amendment to the bill would have also allowed states to impose work requirements on some Medicaid beneficiaries and prevent states that had not expanded Medicaid under Obamacare from doing so in the future.

Mr. Trump cannot unilaterally prevent states from expanding Medicaid in the future. He could, however, allow states to do things like imposing work requirements or charging premiums for more Medicaid beneficiaries, through a process that lets the government waive the normal Medicaid rules.

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

Essential health benefits

What the bill tried to do Let states decide What Trump can do Redefine categories

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.

House Republicans added an amendment to their bill that would have let each state define its own set of essential benefits beginning in 2018.

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

For example, the administration could redefine preventive care in a way that eliminates a current rule requiring insurers to cover every form of contraception that is approved by the Food and Drug Administration.

Employer mandate

What the bill tried to do Eliminate the mandate What Trump can do Not much

The Republican bill tried to eliminate the mandate that larger companies provide affordable insurance to their workers or face financial penalties.

The I.R.S. is charged with tracking company employment records and assessing fines on companies that do not comply. There are some small changes to the system that could be achieved through regulation, but most of the system’s major rules cannot be changed without congressional approval.

Restrictions on charging more for older Americans

What the bill tried to do Charge more for older customers What Trump can do Not much

Under the Affordable Care Act, insurance companies selling policies to directly to individuals cannot charge their oldest customers more than three times the price they charge their youngest ones.

The Republican bill sought to change that ratio so that insurers could charge older customers five times the price for young customers. Unless Congress changes the law, the Trump administration’s options are limited.

Taxes created under the Affordable Care Act

What the bill tried to do Repeal taxes What Trump can do Not much

The Republican bill sought to eliminate taxes imposed under the Affordable Care Act, including taxes on investment income, wages above $200,000, medical devices, prescription drugs and indoor tanning.