Here's a guess:
Value Added Tax: Huge revenue-raiser, which is why Republicans hate it. Value added taxes are very hard to dodge, because it's largely self enforcing: if you don't pay the tax, the people you sell to have to pay it, so they tend to demand proof you've paid. Unfortunately, as with all sales tax variants, it's hard to make the thing progressive; exempting "necessary" goods and services only gets you so far. So it's not very popular with Democrats, either. We may end up with a VAT, but only when we're really desperate.More at the link.