Even if the US lacked refinement capacity (which is obviously not true), significant capital investment as implied by the OP is not something the U.S. lacks.
This for sure. Its far easier to rework a refinery designed for heavy, sour oil and make it ready to process light & sweet. And WTI is very light & sweet. More and more refineries in the US have moved to processing more and more light/sweet crude oil as the level of imports lessened.
