US Democratic presidential hopeful Elizabeth Warren's latest campaign ad attacking billionaires has prompted pushback from some of its targets. The ad to promote Ms Warren and her wealth tax proposal aired Thursday on CNBC, featuring cable TV clips of billionaires criticising her. In response, former Goldman Sachs executive Lloyd Blankfein tweeted: "Maybe tribalism is just in her DNA." In addition to Mr Blankfein, the ad includes footage of hedge fund manager Leon Cooperman, TD Ameritrade founder Joe Ricketts and PayPal co-founder Peter Thiel. "Some billionaires don't like my #TwoCentWealthTax? I'm shocked," Ms Warren tweeted.