Representative Michael C. Burgess, Republican of Texas and a physician, acknowledged that repealing the law became more difficult with each passing week, as various provisions took effect and were woven into “the fabric of American life.”

Michael A. Needham, chief executive of Heritage Action for America, who is leading a campaign for repeal, said, “There will be technical challenges in unwinding the legislation.”

Many Republican candidates for Congress have emphasized their desire to repeal the health care law. Their vow is an election issue, and more  a commitment they mean to pursue, regardless of the election results.

Efforts at repeal face several hurdles:

¶ Not even the most optimistic Republicans expect to gain the two-thirds majorities that would be needed to overcome a veto.

¶ The law responds to a genuine need. The Census Bureau reported last week that 50.7 million people were uninsured in 2009, an increase of 4.3 million or nearly 10 percent over the previous year.

¶ The health care law saves money, by the reckoning of the Congressional Budget Office, so Republicans would need to find ways to achieve equivalent savings if they repealed the law. (The budget office affirmed last month that the law would “produce $143 billion in net budgetary savings” over 10 years.)

¶ While trying to repeal the health care law, Republicans do not agree on what to replace it with.

¶ Popular and unpopular provisions of the law are intertwined and difficult to separate. People like the idea of being able to buy insurance regardless of any pre-existing condition. They dislike the idea of being compelled to do so. But without such a requirement, people could wait until they got sick and then buy coverage  a situation that has proved unworkable in states that have tried it.