In an email, Sarah Lueck of the nonpartisan Center on Budget and Policy Priorities, explained that this “rule allows insurers in the individual market to offer plans with higher deductibles and out of pocket costs in 2018 than have been permitted previously.” Because of this, “the rule is likely to reduce the premium tax credit for many people.” A premium tax credit is a federal subsidy that consumers can use to lower their monthly health insurance payments.

A study the center conducted in February outlines the damage that this rule inflicts on Obamacare by reducing federal subsidies. It found that it would “raise premiums, out-of-pocket costs, or both for millions of moderate-income families.” In addition,

the rule would reduce the amount of health care that marketplace plans have to cover. That would allow individual-market insurers to offer plans with higher deductibles and other out-of-pocket costs than they can now sell through the marketplaces.

Most important, according to the center’s analysis, is the covert aspect of the rule which has

the hidden impact of reducing the Affordable Care Act’s premium tax credits, which help moderate-income marketplace consumers afford health care. As a result, the rule would force millions of families to choose between higher premiums or worse coverage.

Louise Norris, one of the founders of the Colorado Health Insurance Insider, has mapped out the Republican strategy in an online essay, “10 ways the GOP sabotaged Obamacare.”

The attacks began on day one, March 23, 2010, when the A.C.A. was signed into law. Fourteen state Attorneys General, 13 of them Republicans, filed suit challenging the constitutionality of the mandate requiring individuals to buy health care coverage. The sole Democratic Attorney General involved, Buddy Caldwell of Louisiana, switched into the Republican Party in 2011.

On June 28, 2012, the Supreme Court affirmed the constitutionality of the individual mandate but in a blow to the program, Norris wrote, it also

ruled that the federal government could not withhold Medicaid funding from states that did not expand Medicaid. This had the effect of making the ACA’s Medicaid expansion optional, which has, in turn, hobbled the ACA’s progress in many states.

The rejection of Medicaid expansion by 19 states — all controlled by Republican governors or legislative majorities or both — to cover individuals making up to 138 percent of poverty level income meant that these individuals had to turn to “Health Insurance Marketplaces” or “private insurance risk pools.” The addition of low income, Medicaid-eligible individuals in these 19 Republican states to the private A.C.A. insurance market added a less healthy and more expensive-to-insure population to the pool.

Faced with more a costly clientele, insurance companies increased premiums. This gave Republicans new ammunition to charge that Obamacare premiums were rising.

A 2014 measure sponsored by Senator Marco Rubio, Republican of Florida, capped government spending to protect insurance companies against financial losses. It, too, weakened Obamacare. The Rubio amendment, Robert Pear wrote in The Times, demonstrated “the effectiveness of quiet legislative sabotage.”