A relative newcomer to health insurance intends to enter or expand on the Affordable Care Act exchanges in five states at today’s filing deadline, improving the outlook for Obamacare but hardly eliminating the grave threat Trump administration-spawned uncertainty poses.

Oscar Health, started in 2012, joins insurer Centene which last week announced plans to sell ACA plans in Kansas, Missouri and Nevada and to expand in six other states. The news comes as even insurers that have announced their plans to sell ACA plans publicly reserve their right to change their minds.

"We intend to participate but we will continue to monitor for changes at the federal level that could impact our decision on whether to sign the agreement in September," said Mary Danielson, a spokeswoman for Blue Cross Blue Shield Tennessee (BCBST).

The company was the first to officially file to sell 2018 plans in Tennessee and will sell individual insurance in most parts of the state, but not the greater Memphis and Nashville areas.

In an interview Wednesday, Independence Blue Cross CEO Daniel Hilferty said that even though he considers his company to be "the insurer of last resort" in several counties around Philadelphia — where they are the only on-exchange carrier — he’s told his board it may have to pull out if the picture in Washington without certainty about funding of the cost-sharing subsidies and enforcement of the individual mandate.

"For the first time, this has to be wait and see," says Hilferty. "We need adults to get in a room that are willing to look past political ideology and develop a program that meets the needs of as many as Americans as possible."

The Trump administration has refused to commit to reimburse insurers for the subsidies about 7 million consumers get to defray the costs of deductibles and other cost sharing.  It is also not clear that it will enforce the ACA-mandated tax penalty for those who don't have health insurance.  Without that assurance, insurers fear they won't get enough healthy people to sign up to offset the cost of insuring the sick.

Actuaries at the health consulting firm Oliver Wyman estimated last week that two-thirds of the rate increases in 2018 are due to this uncertainy, while ACA supporters including Charles Gaba of ACASignups.net say it's a major reason for the insurer exits. Hilferty says Democrats share some of the blame.

President Trump has suggested the indecision could push Democrats to support the ACA replacement plan being considered behind closed doors in the Senate. But that strategy may be backfiring, a study out today by the University of Maryland’s Program for Public Consultation shows. All of the key provisions of the House-passed American Health Care Act are opposed by clear majorities.

Overall, nearly 70% of 2,430 registered voters surveyed oppose the legislation and more than 60% were against it even in very Republican districts.

Independence is on the exchanges in Pennsylvania and New Jersey, but has Medicaid managed care plans and other insurance business in 23 other states.

"We've always enthusiastically participated in government-funded insurance programs," said Hilferty. "No longer can we trust the government is a good partner."

Oscar CEO Mario Schlosser is more optimistic.

"We're confident that when the dust settles, the market for health insurance will stabilize in time for 2018," Schlosser said in a blog post out today. "For all of the political noise, there are simply too many lives at stake for representatives in Washington, D.C. not to do what's right for the people."

• Tennessee.  In addition to Oscar's entry in the state, BCBST is preparing to re-enter the greater Knoxville market, which was temporarily without an insurer for 2018 after Humana announced plans to exit.  It will not be in the greater Memphis or Nashville areas. Cigna is expected to remain in the market and the insurance commissioner expects that a metro area could see a new entrant.

• Florida.  The state's largest health insurer, Florida Blue, told  the USA TODAY Network earlier this month that it would remain in the individual market in all of the state’s 67 counties for 2018. It and other insurers must officially announce their intention to do so and file their insurance rate requests by Wednesday.

Florida Blue’s decision means that no county will be without an ACA plan, though it’s still unclear how many counties will have to rely on the insurer as its sole individual-market provider.

The company has not said what rate increases it might request. But David Pizzo, Florida Blue market president for the company's west region, said the proposed prices will assume that the Trump administration will leave in cost-sharing reduction payments to insurers.

If those payments end, Pizzo said the company would likely seek to add 20% to premiums, on top of whatever it submits Wednesday.

• New Jersey. Oscar is reentering the state in 2018 after dropping out for a year. The company had one of the broadest networks of hospitals and doctors offered on the state exchange and didn't use tiers, or financial incentives, to encourage members to seek care from preferred providers. That may have attracted older and sicker customers, whose health care costs would have been higher than average.

The company, named after co-founder Joshua Kushner's great-grandfather, was known for its streamlined online portal, witty cartoon ads and use of telemedicine and mobile apps..

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Oscar takes a proactive approach to getting its customers to improve their health. For example, members who hit a tailored number of steps daily for a certain period receives credit to spend on Amazon. It also assigns a four-person team comprised of a nurse and three “care guides” to each member for a concierge-like approach to care.

Its approach echoes broader trends in the industry that urge people to take active control of choices that influence health to be informed shoppers. It  also offers around-the-clock access to a doctor via its smartphone app.

Contributing: Lindy Washburn