So first, take your co-worker aside and emphasize that she is loudly broadcasting views that may not be shared by others. Next, stress that work is not the appropriate venue to subject others to her political beliefs, no matter how passionately she feels. Third, remind her to keep her political opinions to herself, unless she is talking quietly in private conversation with someone who is a willing participant.

These tactics should be enough to end the behavior. But if she objects and purports that she has a right to talk about politics if she wants to, you'll have to take another approach. Allow that while she enjoys a constitutional right to free speech, she doesn't generally enjoy a right to air her views indiscriminately in the workplace.

In fact, a private employer has the right to fire disruptive employees – and provocative verbal statements in the open about political issues could certainly fit most definitions of "disruptive." With any luck, you'll be able to convince her to follow the presidential slogan that William McKinley ran on in 1900: "Let Well Enough Alone."