ST. PAUL — The Trump administration’s efforts to undermine the Affordable Care Act have health care advocates and insurers concerned that the open enrollment period will be one of chaos and confusion.
But not all applicants will be affected in the same way. A dozen states, including Massachusetts, operate their own health insurance marketplaces, maintaining control over advertising and the help they can offer consumers.
That will create a striking difference when open enrollment begins Wednesday between those states and the others that rely on the federal marketplace, essentially creating a tale of two countries.
For the individual health insurance market in much of the country, the Trump administration has slashed spending on advertising by 90 percent and drastically reduced budgets for the groups that help consumers choose a plan.
It cut the open enrollment period in half, to six weeks. Shortening the sign-up window further, the federal government will shut down its online marketplace, healthcare.gov, for 12 hours of maintenance nearly every Sunday during open enrollment.
The 12 states with their own exchanges are free to chart their own course and make it easier on consumers. Nine have extended open enrollment beyond Dec. 15 — by a week in some states and six weeks in others. The Massachusetts enrollment period will end Jan. 23.
The states also can make their own decisions about spending because their budgets are free from Washington politics. State-run exchanges typically pay for their operations through fees charged to insurers on plans sold through their marketplace.
Minnesota, Colorado, and Washington will continue heavy advertising for their exchanges. Thousands of enrollment specialists will continue to help consumers navigate insurance plans in California and New York.
For many of these states, 2018 looks like a payoff for the political risks and costs they assumed when they decided to set up their own exchanges.
‘‘When I think about what’s going on at the federal level, I’m sure glad we have the reins here at the state,’’ said Allison O’Toole, director of Minnesota’s health insurance exchange, MNsure.
With the help of a separate and costly state program that is keeping premiums stable for 2018, O’Toole said she thinks Minnesota’s exchange may be on track for its best year yet.
No state is totally immune from the spikes in insurance premiums since the health care overhaul launched in 2014.
Many states are bracing for double-digit rate increases in the individual market, from an average increase of 12.5 percent in California to jumps of roughly 45 percent in Florida and nearly 60 percent in Iowa. Premiums for the most popular plans are up 34 percent nationwide, on average.
Millions of shoppers, whether they buy coverage on healthcare.gov or through their state’s marketplace, will see another modest spike after Trump’s decision earlier this month to halt payments to insurers that help cover some consumers’ deductibles and co-pays. Trump called those cost-sharing payments ‘‘bailouts’’ to insurance companies.