Barack Obama has been known to use his middle finger to scratch various parts of his face while he is speaking. Often this seems to happen just as he mentions the name of someone he has tangled with in some way or another. Now Rush Limbaugh has modified the gesture metaphorically:
In case you are not clear on the scratch technique, here is a screen grab reminder:
Even fellow Democrats can be targets, like Bethlehem, Pennsylvania Mayor John Callahan who had once backed Hillary Clinton's presidential bid:
Freedom's Lighthouse has another example here.