U.S. security is intimately tied up with global security. Of course it is always proper to examine our overseas bases for efficiency and efficacy in light of the mission(s). But global security is a major component of our mission.
We had no bases in Ukraine or Crimea, and events there undermine global security and U.S. security. Pulling all our forces out of Iraq left a military vacuum which was taken advantage of by forces that undermine U.S. security.
America has always had isolationist tendencies. It’s a mistake to let those tendencies play a part in our global missions.