President Trump's new executive order instructing federal agencies to grant relief to constituencies affected by the Affordable Care Act has begun to reverberate throughout the nation's health-care system, injecting further uncertainty into an already unsettled insurance landscape.

The political signal of the order, which Trump signed Friday just hours after being sworn into office, was clear: Even before the Republican-led Congress acts to repeal the 2010 law, the new administration will move swiftly to unwind as many elements as it can on its own - elements that have changed how 20 million Americans get health coverage and what benefits insurers must offer some of their customers.

But the practical implications of Trump's action are harder to decipher. Its language instructs all federal agencies to "waive, defer, grant exemptions from or delay" any part of the law that imposes a financial or regulatory burden on those affected by it. That would cover consumers, doctors, hospitals, and other providers, as well as insurers and drug companies.

The prospect of what could flow from pulling back or eliminating administrative rules - including no longer enforcing the individual mandate, which requires Americans to get coverage or pay a penalty, and ending health plans' "essential benefits" - could affect everything from how many people sign up on the ACA marketplaces before the current open enrollment ends Jan. 31 for 2017 coverage to how many companies participate next year.

Robert Laszewski, president of the consulting firm Health Policy and Strategy Associates, called the executive order a "bomb" lobbed into the law's "already shaky" insurance market. Given the time it will take to fashion a replacement, he expects that both federal and state insurance exchanges will likely continue to operate at least through 2018.

"Instead of sending a signal that there's going to be an orderly transition, they've sent a signal that it's going to be a disorderly transition," said Laszewski, a longtime ACA critic. "How does the Trump administration think this is not going to make the situation worse?"

Trump adviser Kellyanne Conway said Sunday that the president may stop enforcing the ACA health insurance mandate, even before Congress repeals the law. "That is something that is really strangling a lot of Americans, to have to pay a penalty for not buying government-run health insurance," Conway said on ABC's This Week.

Teresa Miller, Pennsylvania's insurance commissioner, said Saturday that several insurers on her state's exchange "considered leaving the market last year" and that Trump's action could propel them to abandon it in 2018. "When I saw the executive order . . . all I kept thinking was this just creates more uncertainty and adds more instability to this market," she said.

As of this year, nearly a third of all counties nationwide already have just one insurer in the federal marketplace, and almost two-thirds of counties have no more than two insurers.

On Capitol Hill, Republican leaders are offering cautious praise for the president's executive order. Yet more broadly, the GOP remains in a state of uncertainty on health care, with unresolved questions about the path forward.

Sen. Lamar Alexander (R., Tenn.), chairman of the Health, Education, Labor, and Pensions Committee, was briefed on the details of Trump's order only Thursday, according to a GOP aide who spoke on condition of anonymity to describe private talks.

Alexander said in a statement late Friday that Trump was "right to make the urgent work of rescuing Americans trapped in a collapsing Obamacare system a top priority on his first day in office."

Senate Majority Leader Mitch McConnell, (R., Ky.), speaking on Fox News Sunday, focused on what Trump could do through executive action. "President Obama implemented a lot of Obamacare himself, so President Trump will be able to undo a lot of it himself," McConnell said.

Democratic leaders, however, are casting the executive order as evidence that Republicans are in a state of disarray on health care.

"They don't know what to do. They can repeal but they don't have an plan for replace," Senate Minority Leader Chuck Schumer said on CNN's State of the Union. "The president's executive order just mirrored that."

This article contains information from Bloomberg News.