The political Left does not recognize the Constitution as the supreme law of the land (where applicable). They find that the Constitution doesn't include things they want (a right of privacy, right to abortion, etc), says things they don't like (right to keep and bear arms), and has this troublesome Tenth Amendment thing, that prevents the Federal Government from getting involved in, and taking over, anything the ass-holes in Washington want to get involved in. So they swear to protect and defend the Constitution, but what they really mean is that they will fight to maintain the "Constitution," as they imagine it should be. Exhibit A, if you want one, is President Barry Soetoro, who proclaimed publicly on a dozen occasions that he did not have the power under the Constitution, as President, to protect the so-called "Dreamers" from government action to deport them...then went ahead and did it anyway. What value would you place on his oath to protect and defend the Constitution? Less than Zero?
And in case you didn't pick up on it, the Federal Bureaucracy is a part of the Democrat/Leftist Party.