Data: Federal Reserve; Chart: Neil Irwin/Axios Incoming Federal Reserve chief Kevin Warsh's ambition to shrink the central bank's multitrillion-dollar bond portfolio may quickly run into hard limits. Why it matters: For nearly two decades, the Fed's ability to flood markets with liquidity has been among its most powerful crisis-fighting weapons — and, in Warsh's view, too often a go-to tool for monetary stimulus outside of crises. Now, the hot discussion among Fed officials and commentators is