on the borderline
In an uncertain position just before some possible status, condition, action, outcome, etc. The two countries have been on the borderline of full-out war for the past decade. I was on the borderline of quitting before the boss gave me assurances that my complaints would be addressed.
on the borderline
in an uncertain position between two statuses; undecided. Bill was on the borderline between an A and a B in biology. Jane was on the borderline of joining the navy.