Wall Street Journal (may be gated):

• During the 2020 campaign Mr. Biden promised to work toward a policy in which the sole purpose of the U.S. nuclear arsenal would be to deter an enemy nuclear attack.
• Mr. Biden’s new decision, made earlier this week under pressure from allies, holds that the “fundamental role” of the U.S. nuclear arsenal will be to deter nuclear attacks.
• That carefully worded formulation, however, leaves open the possibility that nuclear weapons could also be used in extreme circumstances to deter enemy conventional, biological, chemical and possibly cyber attacks, said the officials.