It’s been exactly one year since President Obama signed a sweeping federal health care law, and with Republicans determined to undo it, Obama knows his 2012 re-election will be a tough referendum on himself and his signature legislation.

Last month, conservatives from all over the country gathered in Washington at the group’s biggest convention, CPAC, uniting behind potential Obama opponents and the call to repeal his law.

“Repeal Obamacare. That would be a good win,” cheered former Pennsylvania Sen. Rick Santorum...