attack dog
US /əˈtæk dɔːɡ/
UK /əˈtæk dɔːɡ/
1.
a dog trained to attack on command or to defend a person or property
:
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The security guard had an attack dog with him.
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They trained the German Shepherd to be an effective attack dog.
2.
a person or group that aggressively criticizes or attacks an opponent, especially in politics or business
:
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The senator's opponent used his campaign as an attack dog.
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The media often portrays certain commentators as political attack dogs.