A number of largely Republican-led states that gambled on delay now face the unsettling prospect that the federal government could take over their responsibilities, particularly in setting up the health insurance marketplaces known as exchanges. Under the law, individuals must be able to buy insurance coverage through the new state exchanges by Jan. 1, 2014. But a more immediate deadline is less than six months away, on Jan. 1, 2013, when states must demonstrate to the Department of Health and Human Services that the exchanges will be operational the next year.