Officially, the Federal Reserve is trying to stay out of the political debate in Washington over tax reform and other fiscal measures. But with so much on the line for the economy, and with the outlook for fiscal policy growing more unclear, Fed officials in practice have been unable to stay mum. In interviews, speeches and even official documents, the Fed has increasingly been weighing in. The minutes of the May policy meeting noted that, "A number of participants pointed out that clarification of prospective fiscal and other policy changes would remove one source of uncertainty for the economic outlook." That's Fedspeak for it's hard to forecast when you don't know what policies will be and we'd prefer if you got on with it. The minutes also say Fed members "view the possibility of expansionary fiscal policy changes in the United States as posing upside risks to their forecasts for U.S. economic growth." Translation: If you do it, it could be good. About half of the members of the Federal Open Market Committee have upgraded their forecasts in anticipation of those policies. Many Fed officials, like many economists, support tax reform if for no other reason that it's doctrine in the economics world that taxes distort decision making. Any kind of reform that reduces those distortions — for example by reducing write-offs or simplifying the code — will be seen as a positive for growth. Deregulation gets good reviews for similar reasons. But many Fed members have made no secret that they see the full package of President Donald Trump's economic proposals as a potential mixed bag, in part because it runs afoul of other basic tenets of economics.

Cleveland Fed President Loretta Mester is concerned about immigration reform. She said in a recent speech that immigrants make up 16 percent of the US workforce. "Given U.S. demographics, immigrants will become an increasingly important source of labor supply for the U.S.," she said. "This suggests that a well-thought-out immigration policy that attracts labor to the U.S. is also a necessary ingredient to support longer-run growth." Translation: You need workers to grow the economy and you can't do that if you keep workers out. Dallas Fed President Robert Kaplan singles out health care reform as a potential negative if it reduces the number of insured Americans. That, in turn, could reduce spending and increase savings, he said.

"The reality is, some of the policies being discussed will help GDP: regulatory review, if it's thoughtfully done, potentially infrastructure spending if it's thoughtfully done, could help," Kaplan told CNBC in an interview Tuesday. "But some of them could hurt GDP growth." Trade is another area of concern. In a CNBC interview in March, Fed Vice Chairman Stanley Fischer noted that free trade "worked spectacularly for China (and) it worked for us." "We've been able to buy many, many things that we wouldn't have been able to make had it all been up to us," Fischer said. "So we benefit from that as well. … I'd be concerned if that basic model is overturned."

Doubts about tax cuts