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, where people will be able to choose among policies for their coverage.

Scott Walker, of course, doesn’t think federal law applies to him.

Mr. Walker quickly raised the risk by announcing that, in spite of the ruling, he would continue to delay any imposition of the law while waiting to see whether Republicans took control of the White House or Congress in November. Republicans on Capitol Hill, and the party’s presumptive presidential nominee, Mitt Romney, have vowed to repeal the entire law if they gain power.  “Wisconsin will not take any action to implement Obamacare,” Mr. Walker said in a statement.