A team of national security officials has been assigned to sketch out responses if President Vladimir V. Putin unleashes chemical, biological or nuclear weapons.
Senator Robert Menendez exerts a powerful influence over U.S. foreign policy, but an uneasy one. A nuclear deal with Iran could strain ties even further.
The Eastern European countries had sought to buy Pegasus, spyware made by an Israeli firm, to carry out intelligence operations against Russia, according to people with knowledge of the discussions.