Wiktionary
grind down
vb. (context idiomatic transitive English) To weaken someone's morale over a long period.
WordNet
Usage examples of "grind down".
He taps away at his spark key as the green helix spins in the lower-left corner of my visual field, and information tools grind down data in the recesses of my skull.
To grind down, to slowly, slowly abrade and at the same time fuse, wearing away and seizing up at once, like sand-laden water in some huge engine.
They had to do more than slowly grind down the enemy through bomb.
I grind down a long slope, dozing aside rock-chunks jolt-ing across crevasses.
The best prediction of the outcome that Claire Normandy could now get from her computers was that the battle would most likely grind down to something like a draw.