Warren Buffett is ready to call Republicans’ tax bluff. Last fall, Senator Mitch McConnell said that if Buffett were feeling “guilty” about paying too little in taxes, he should “send in a check.” The jab was in response to Buffett’s August 2011 New York Times op-ed, which made hay of the fact that our tax system is so unbalanced, Buffett (worth about $45 billion) pays a lower tax rate than his secretary. Senator John Thune promptly introduced the “Buffett Rule Act,” an option on tax forms that would allow the rich to donate more in taxes to help pay down the national debt. It was, as Buffett told me for this week’s TIME cover story, “a tax policy only a Republican could come up with.”