Two years later, that decision has taken on new prominence after Chief Justice John G. Roberts Jr. accused Mr. Obama from the bench on Wednesday of not having ''the courage of his convictions'' for continuing to enforce the marriage law even after concluding that it violated constitutional equal protection guarantees. The chief justice's needling touched a raw nerve at the White House. ''Continuing to enforce was a difficult political decision,'' said an aide who asked not to be identified discussing internal deliberations, ''but the president felt like it was the right legal choice.''