NEW: DHS Secretary Markwayne Mullin & Sen. Chris Murphy (D-CT) already tangling in Senate hearing.
Murphy used his opening statement to say DHS is violating the law and Constitution every day.
Mullin responds: "You're looking for soundbites, you weren't even looking at me, you were looking at the camera...the outlandish claims you made are flat out wrong...we're enforcing the laws Congress passed. What's unconstitutional? For you to throw my 275,000 employees under a broad stroke like t hat is reckless and irresponsible."