How can I respond to Whataboutism?

While this uses examples that could be seen as supporting one side or the other, it is intended as a politically neutral question, to the extent that that is possible

This has come up more and more in political discussions I've been having recently, mostly to do with the American election. Basically, whenever a point is brought up, it's not really addressed, and is countered with something that the other candidate has done, or a slur against the other candidate.

E.g. If Donald Trump's racism is brought up, a response I've heard is that Hillary Clinton is also racist. Another one I've heard is attacking Obama's policies on illegal immigration in response to an attack on Donald Trump's policies (e.g. his "wall").

These are just examples, and the accuracy, or not, of the counterpoint is not the issue, the issue is that the counterpoint doesn't address, or attempt to defend against the point made. This makes it very difficult to have a level-headed political discussion without it degenerating into "Donald Trump did this", "So did Hillary Clinton" and vice-versa.

So my question is this:

How can a meaningful political discussion be had with someone who uses Whataboutism extensively?