Google searches and Gatherer failed to inform me, so thanks in advance!

Opponent has a TNN equipped with Jitte (2 counters).
I have a Forcefield and an untapped land that taps for mana.

Does Forcefield need pumped into it each time my opponent removes a counter to give TNN +2/+2, or does the paid reduce the power to 1 as damage would be dealt without leaving an additional opportunity to pump the creature?