WASHINGTON – Nineteen states have turned down the Obama administration's invitation to run the new health insurance markets that will begin serving millions of uninsured Americans less than a year from now. That puts a huge task on the feds, a defining challenge for President Barack Obama's second term.

Friday is decision day for states to notify Washington if they will set up their own insurance exchanges under the federal health care law. Monitoring by The Associated Press finds a divided nation moving ahead, despite the misgivings of some state officials. Half the states now say they will participate in some way.

Still, drafters of the law did not anticipate that so many states would remain on the sidelines at this late stage. Federal control of the new state markets where individuals, families and small businesses will shop for taxpayer-subsidized private coverage was seen as a failsafe, not the standard for nearly half the country. Critics predict delays.