During the presidential campaign, one key difference between Mr. Obama and his chief opponent, then-Sen. Hillary Rodham Clinton, was that Mrs. Clinton‘s plan required all Americans to purchase insurance and Mr. Obama‘s did not.

In 2008, then-Senator Obama supported a health care reform proposal that did not include an individual mandate because he was at that time strongly opposed to the idea, stating that, “If a mandate was the solution, we can try that to solve homelessness by mandating everybody to buy a house,'

Congress eventually included the individual mandate in the bill it passed, and Mr. Obama signed that into law in March. Since then, he and his administration have defended its constitutionality, arguing the mandate is the linchpin that brings in more customers to insurance companies, which in turn allows those companies to expand the availability and lower the cost of coverage.