IF there were years where mitt paid no taxes, that's perfectly legal - he's a smart wealthy man and shouldn't be punished for working the system.
THis is obama playing smart politics. Making romney's biggest strength - his time at bain - into his biggest flaw.
kinda how war hero john kerry was destroyed by the swiftboaters. Every time someone brouhgt up his war services, we were instantly reminded of it.
NOW - in the debates, romney really can't keep saying "During my time in the private sector at Bain..." without most people instantly thinking of the outsourcing and what we now know to be a lie about when he left the firm. He was at board meetings, he was the CEO, he was signing documents... if anything, he was part-time, but he certainly never left the firm.
So his biggest strength - economic prowess- has been weakened.