I didn't post anything during the presidential debate last night, because I watched it without the benefit of an internet connection. Also because bona fide live-blogging can be seriously annoying to read. But if you want it in digest form, here's how I reacted in front of the TV.
Now, it's not clear whether he means tax liability or taxable income. As Dylan Matthews explains, that's the difference between a highly progressive (in the technical sense, not the euphemism-for-liberal sense) proposal and one that would affect a lot of middle-class households.