can we say, "dent in national debt"?

According to the calculations of my union, the UAW -- admittedly, not an impartial source -- if the 400 richest U.S. taxpayers paid the same tax rate on their investment income, which is where most of their money comes from, as they're supposed to pay on their earned income, that would generate $18 billion in revenue.  Needless-to-say, they don't: the top tax rate on income is 35%, but the top rate on capital gains is 15%.  The UAW notes that 15% is what a working couple earning $50,000 pays.