Undermine

To weaken or bring to ruin

That guy at work is always trying to undermine me with the boss.

The term undermine comes from way back in the day when a military forced besieged a castle or walled town, the main goal was to breach the walls.

At first this was done by having sappers get close to the wall and either set fire or later place explosives next to it. When moats, deep ditches filled with water surrounding the walls, came into play this got more difficult as they could not get as close.

One way around this was to dig tunnels starting from he other side of the moat and leading to the foundations of the wall. There they would either start fires and allow the heat to crack and damage the wall from underneath, or later they would set off explosions below the foundations hoping to bring he walls down. This became known as undermining.