With the drop in oil prices from the past years, getting oil out of the ground in the US became too expensive. A lot of newly installed sites were closed because they could only operate efficiently with an oil price near $80 a barrel. I am quite sure the US imports a lot of oil...

Edit: quick results from 2015: 25% is imported. https://www.eia.gov/tools/faqs/faq.cfm?id=32&t=6

Isn't that part of why Republicans are pushing for increased exploration/extraction in many of the public lands found in the west/Alaska?

And when resources start running out elsewhere, it will eventually shift back, that isn't necessarily a bad thing.

A lot of oil is imported for the refineries to process.

https://stateimpact.npr.org/texas/2014/10/28/why-is-the-u-s-...

I stand corrected