conditional
I think it may not be necessary, and also dpends what things are looking like during the primaries. We need to focus more on spreading the word, recruiting, and ensuring a VERY high percentage turnout to the polls of supporters to maximize our impact.
*IF* there was to be one, I think Martin Luther King day (vision, inclusiveness, rights, equality, not to mention a statement within the Republican party and a slap in the face to the white supremicist crap), or Presidents Day (tradition, founders, patriotism) are both prime targets, although MLK has the advantage of being very well positioned going into super tuesday (last minute ad push and also a possible bump in media attention, although at that point it might be a polical frenzy).
I guess if I had to pick one I would say MLK, but again, it might not be necessary.