The next Congress faces a stunning array of challenges — on health care, gun policy, climate change, you name it. One crucial challenge starved of attention, however, is what I call runaway inter-generational wealth. That’s where the wealth of a country’s richest families snowballs from one generation to the next, unconstrained by living expenses or taxes, causing an ever-increasing share of national wealth to concentrate at the top. America has experienced this problem for decades now, and last year’s tax act is certain to make it worse. For the first time since the estate tax was enacted a century ago, rich American couples can pass $22 million to their children entirely free of federal taxes.