It's often said that good things come to those who wait — but a bloated $4.5 trillion balance sheet might be a notable exception to that rule.

With the Federal Reserve facing a Herculean conundrum in unwinding its crisis-era monetary policy — and a likely leadership transition on the horizon — Goldman Sachs suggested on Saturday the central bank could move early to reduce the vast sums of government and mortgage-backed securities (MBS) it holds on its books. In a research note to clients, the bank pointed to the likelihood that President Donald Trump may "reshape the leadership" of the Federal Open Market Committee (FOMC), the Fed's powerful policy-making body, as the terms of Fed Chair Janet Yellen and Vice Chair Stanley Fischer expire in early 2018. "This could be important for balance sheet policy because many Republican-leaning economists have criticized quantitative easing (QE) and have expressed a preference for rapid balance sheet rundown, perhaps even through asset sales," wrote Daan Struyven, a Goldman economist. If the new appointments—especially the new chair—are thought to favor aggressive balance sheet normalization, perhaps even including asset sales, and if all decisions are left up to the incoming team, financial markets might experience heightened uncertainty during the transition."

Goldman suggested there was a "strong 'risk management' case for an announcement of very gradual balance sheet runoff later this year," because of the political risk associated with new leadership at the Fed. "Our forecast is that the discussion around reinvestment continues for most of this year and the plan is formally announced in December 2017," Struyven said. "At that meeting, we expect the committee to hold the funds rate steady after hiking in both June and September. We expect the quarterly hikes to resume in March 2018." The economist harked back to 2013's "taper tantrum," in which markets reacted the Fed's suggestions of tighter monetary policy by sending bond yields surging and stocks reeling — albeit temporarily.

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A potential fire sale of Treasurys and mortgage-backed securities by the Fed "could have significantly more adverse effects on financial conditions than gradual runoff, and the mere risk of such an outcome might set up another 'taper tantrum,' " Struyven added.

'The uncertainty is substantial'