President Barack Obama challenged Republicans on Friday to spell out their plan for replacing his signature health law, insisting he’s open to new ideas, but casting doubt on what his political rivals can muster. “If it works, I’m for it,” Obama said during an interview with Vox, adding he would only support a Republican plan if it contains the protections that he included in the Affordable Care Act, such as barring insurance companies from withholding coverage for Americans with pre-existing conditions.