President Biden repeatedly insists that his infrastructure plan will create millions of jobs and labor unions will be the big winners. But interviews with economists, union leaders, government officials and trade groups as well as basic math suggest otherwise. The once-dominant trade and construction unions no longer have enough members outside of their strongholds on both coasts and in the Midwest to claim most of the projected infrastructure jobs. By some estimates, two-thirds of these jobs will go to nonunion workers who dominate the construction markets in most states. Biden, in short, appears to be harking back nostalgically to an era of union strength in the private sector that is decades gone. “It’s going to be really hard for unions,” says David Macpherson, an economist at Trinity University who specializes in organized labor. “I expect they would get far less than half of the infrastructure jobs.” In addition, the overall …