Concern about protectionism from President Donald Trump is clouding the outlook on Wall Street, with respondents to the January CNBC Fed Survey saying trade policies could overshadow the effects of the administration's pro-growth plans.

Protectionism is seen as the No. 1 threat to U.S. expansion by 51 percent of respondents, almost double the percentage from the December survey and the first time in the survey's history that any single concern has been expressed by a majority. It eclipses the 44 percent who were worried about global economic weakness early in 2016 -- concerns that sent markets into a nosedive.

"Investors can get behind pro-growth policies and can't and won't support protectionist policies," Art Hogan, chief market strategist at Wunderlich Securities, said in response to the survey. "Trade wars, like all wars, end negatively for all."