Donald Trump has issued a proclamation that temporarily suspends the entry of applicants for an immigrant-visa. The suspension will be effective as of April 23rd 2020 23:59 EDT and, unless it is modified or extended, will last for 60 days. This order does not affect people applying for a temporary visa like H-1B, L-1 or other nonimmigrant categories. It specifically excludes certain groups, amongst others lawful permanent residents of the U.S., spouses or unmarried children of U.S. citizens if the children are under 21 years old, or individuals whose entry to the country is of national interest.
The proclamation only applies to immigrant visa applicants, unless they already have a valid visa as of the effective date. If they have another type of travel document like e.g. a boarding foil, a transportation letter or advance parole, they will also be allowed to travel to the US.
The order is likely to not have much effect, as most of the US consulates have already suspended routine visa operations abroad. However, there could be additional delays even after the consulates take up their visa operations again. The proclamation is also directing federal agencies to review the immigrant programs within the next 30 days and to recommend additional measures.