Nanosecond-laser-induced damage measurements in the bulk of ${\mathrm{KTiOPO}}_4$ (KTP) crystals are reported using incident $532\mathrm{nm}$ light or using incident $1064\mathrm{nm}$ light, which pumps more or less efficient second harmonic generation. No damage threshold fatigue effect is observed with pure $532\mathrm{nm}$ irradiation. The damage threshold of Z-polarized light is higher than the one for X- or Y-polarized light. During frequency doubling, the damage threshold was found to be lower than for pure 1064 or $532\mathrm{nm}$ irradiation. More data to quantify the cooperative damage mechanism were generated by performing fluence ramp experiments with varying conditions and monitoring the conversion efficiency. All damage thresholds plotted against the conversion efficiency align close to a characteristic curve.