As the parent comment explains, the US can't produce all the oil it needs, because it's refinery capacity isn't aligned with the type of oil it pumps from the ground.
I have seen a few slightly different figures but it is something like 40% of oil still needs to be imported to get the right mix for the current economic setup.
It can be if necessary. It’s just the US refineries can deal with the crappy oil produced by places like the tar sands in Canada, where few other countries currently can