Democrats are weighing their options for taxing the ultrawealthy. : By Andrew Ross Sorkin, Jason Karaian, Sarah Kessler, Stephen Gandel, Michael J. de la Merced, Lauren Hirsch and Ephrat Livni No one is better equipped to mount a constitutional challenge to a proposed tax on the unrealized capital gains of the ultrawealthy than, well, the 700 or so billionaires who may face the tax.