the.com/undermining
Sabotage with a smile, demolition that prefers no fingerprints on the wrecking ball.
means Quietly weakening someone or something through small, deniable acts rather than open confrontation.
from From medieval siege warfare: attackers literally dug tunnels under castle walls, then collapsed them to bring the fortress down without a frontal assault.
Literal sappersTunnel-diggers were called miners, hence the word.
Office variantCompliments engineered to leave a bruise.
Geology cousinRivers undermine cliffs the same patient way.