Example with a context (Vox news story: The real costs of Donald Trump’s anti-Mexican slur controversy, explained):
Liberal Latino and immigration advocacy groups, on the other hand, are happy to treat Trump as a serious Republican candidate, for the purposes of demanding that other Republicans and the RNC distance themselves from him. They're treating Trump as the Republican id: He expresses racist feelings that some liberals suspect many Republicans secretly harbor but lack the cojones to say out loud.
Left-leaning Latino and immigration advocates treat Trump as the id of white conservatives, saying things that Ted Cruz, for example, wouldn't say.
How do you exactly understand this type of figure of speech?