On March 12th, President Trump imposed a ban on any person with a visa from traveling into the U.S. if they are from or have been in a Schengen country in the 14 days prior to their attempted entry to the U.S. Schengen countries include 26 European countries. There are a number of exceptions to the entry ban (including all persons who have had at least a 3 night stay at a Trump resort and/or played a round of golf or at least I think that is in there). The ban applies to all non-immigrant visas and new immigrant visas and is expected to last 30 days. A copy of the proclamation can be found here.
Update 3-16-2020 UK and Ireland have been added to the entry ban.