RAMSTEIN AIR BASE, Germany — Dozens of uniformed officials looked to the head table Thursday morning at the dimly lit officer’s club here. They were staring at Lloyd Austin, America’s secretary of defense, the man who brought them all together. But as the day began, the focus was less on Austin than what it means for him to depart.

Even as Russia seems to have the upper hand in its invasion of Ukraine, the Kremlin faces a growing number of challenges that will complicate any effort to lock in its gains, the outgoing Pentagon chief said.