One sign of good mental health is the establishment of proper boundaries - boundaries around yourself, your property, and your relationships. Boundaries around yourself help keep you focused on your priorities without kowtowing other people's demands and expectations.
Boundaries also help identify the things and the people that are most important to you, and they indicate your commitment to protect those things and people. That's not to say you won't act to protect others or their property, but you will only do so after you have fulfilled your responsibility for those within your boundaries.
What does all that have to do with public policy? Well, all those benefits of boundaries around people are applicable to nations as well. Boundaries for countries, which we call borders, identify the property and people the nation is obligated to protect. That's not to say we won't help others, but we should only do so if we have first fulfilled that responsibility to our own citizens. And, regardless of the demands and expectations of others, we should focus on being what America is supposed to be - a nation built on the principles of liberty.