It was. NASA still flies T-38s as astronaut trainers and taxis. And as photo chase planes at Edwards.
T-38s are about to be phased out from pilot training, or already have been. They had a 50+ year run at that job and the airframes are getting pretty tired.
Somebody up above asked about the F-5 and F-20. The F-5 was a single-seat version of the T-38, with some basic weapons capability. It was used as an export fighter to Vietnam and some other smaller countries but never adopted here. The F-20 was a single-seat and single-engine version of the same, with much improved performance, better weapons, and a decent radar. It was never bought by the AF at all and they only made a few demonstrator copies. You can WIKI both of them for more detail.
