He wasn't. He'd had Triumph and MG factory backing since the start, then British Leyland, and somehow turned the XJS into a Trans Am winning car, and the TR8 into a dominant one.
Jag then wanted him to take Jag to the top of world endurance sports car racing, but he never could quite deliver. Turned out beautiful cars that were PRETTY competitive, but never enough to win a crown jewel (24 hours of Daytona or Lemans).
TWR did that for Jag, have to admit that.
Tullius went back to Trans Am with Audi and then to NASCAR for a year with Pontiac before throwing in the towel.