Do not give them any of your time,
ignore them if possible and go about your daily business,
pretend not to hear, understand their questions or answer a completely different question (favorite lefty tactic BTW)
DO NOT provide them any courtesy such as water, coffee, desk, chair, etc.
pretend they are invisible
These tactics have been used against "government assistants" in the past and the eventually get bored and leave. These morons are used to getting major attention and can't cope with being ignored.
If the Gestapo was the German Nazi secret police, is the DHS the DHStapo?
And I’d ensure that any coffee they obtained was laced with laxatives, the tires on their car would be flat every day, etc etc etc.