Sen. Joe Manchin broke ranks with the Democrats on Wednesday, saying he would vote against President Barack Obama’s pick to lead the Federal Energy Regulatory Commission, Ron Binz, a move that could sink the nomination. The surprise decision by the coal-state Democrat is the latest twist in power struggle over the chairmanship of the agency that typically draws attention only from power sector and pipeline wonks. But the Binz nomination has recently jumped to the editorial pages of The Wall Street Journal as conservatives attacked a regulator they view as hostile to fossil fuels. Manchin’s move crimps the Democrats’ 12-10...