The "brunt" of an impact or blow is the principle or main part of it; most of the force and damage of a blow or attack. To "bear" this is to sustain it, to be the target of it.
Example: "Banking stocks bore the brunt of today's damage on Wall Street, with retailers suffering relatively mild losses." (Here, the idiom is in the past tense)
In this example, the damage is purely financial, but this idiom can be used for politics, war, or any other situation where violent forces - literal and figurative - are at work. A particular street can bear the brunt of a tornado, for example.