Ankara may buy Moscow’s most advanced Su-57 after its expulsion from the F-35 program.
The administration has settled on a package of sanctions to punish Ankara for buying a Russian missile system.
The latest breach could significantly reduce the time it will take Tehran to amass enough weapons-grade uranium for a nuclear weapon.
Turkey is set to receive the first of its Russian S-400s in days.
The candidates also sparred about the 2015 Iran nuclear deal and the war in Afghanistan.
The U.S. military launched cyberattacks against Tehran in response to the shootdown of a U.S. drone.
Mark Esper, who takes over as acting defense secretary on Monday, won’t have time to catch his breath before his first major appearance in the job.
New security agreement rewards Poland’s commitment to defense spending.
Decision to start ‘unwinding’ Turkey from the F-35 fighter jet program is the latest sign of strained ties between the two nations.
A bipartisan group of senators vowed to block the administration’s move to bypass Congress and expedite an $8 billion package.
The debacle threatened to overshadow Patrick Shanahan’s first major speech on the international stage.
The tete-a-tete on the sidelines of Asia’s leading security summit comes as Washington and Beijing clash on issues from cybersecurity to trade.