Republican leaders in the Senate stepped in Wednesday to block Sen. Rand Paul’s latest effort to defund Planned Parenthood, an issue popular with the GOP base that some say could help energize voters for the midterm elections. The Kentucky senator late last week signaled that he would offer an amendment to the appropriations bill funding the departments of Labor and Health and Human Services, the relevant legislative vehicle for the Planned Parenthood funding ban. Supporters said that it would need just a majority to win. Late Wednesday, Paul moved to add his amendment to an opening on a so-called “amendment...