In interviews this week, Walker and his top political advisers provided the fullest account yet of his plans for the likely rollout of a national campaign. The 47-year-old Republican intends to use an upcoming legislative session in Wisconsin to push an ambitious agenda that could, in combination with his triumphs over Big Labor, bolster his standing with Republican primary voters: Repealing unpopular Common Core standards, requiring drug tests for welfare beneficiaries and cutting property taxes.