SINGLE PAYER: If Democrats make little progress on alternatives, some purists might decide it’s best to just renew the case for a single-payer system in which all Americans receive health care paid for by the government.

Sidney M. Wolfe, the director of the Health Research Group at Public Citizen, an advocacy group, has been pushing for government-run health care for decades.

In an interview Tuesday, Mr. Wolfe said a ruling against the current law could help spark a renewed drive for a system that essentially expanded Medicare into a program for everyone, not just the elderly.

“If this is what happens, it may offer more incentive to say let’s decide once and for all that health care is a right,” Mr. Wolfe said. “It will certainly present an opportunity to a number of people.”