When someone is described as being "vulnerable to charge," it typically means that they are susceptible to being accused of something. There are a number of synonyms that could be used to convey this same idea. For example, someone might be described as being "liable to accusation," "susceptible to blame," or "prone to being charged with wrongdoing." Other potential synonyms might include "exposed to allegations," "at risk of being accused," or "open to criticism." Ultimately, any of these terms could be used to express the idea that someone is easily targeted for accusations or charges of a certain nature.