"To bird-dog" means "to follow, watch carefully, or investigate." When used in a political context, the term refers to activists who seek out candidates or elected officials, pin them down with specific questions or information, and retrieve their views. It is also known as “direct candidate engagement.” 
Bird-dogging is attending elected official’s (aka your target) events and public appearances and directly asking them about their stance on an issue or to support your cause. It really is all about getting our elected officials to stop hiding on the issues and force them to either take a stance or make it clear they’re deflecting questions from constituents. Repeated questions and asks on a particular issue also puts it to the forefront of their mind and shows that constituents/community members care about it. 
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