I think a little differently about this. Yes we think these things, but Trump is seriously off- track. Personal attacks are made when someone is working from a position of weakness. Instead of this, which will galvanize his voting base, focus on the flip- flopping, the sheer absence of leadership in every aspect of the Office, the total disregard for The Constitution. Remember you are talking about the cult of personality here.. it does not respond logically.... it only responds when it is personal.. to them, not to him. He was perfectly happy to be a one term Prez, to make room for Hillary.
Not when it comes to the so-called independent or moderate voter -- the voter who might have voted Republican in 2008 but decided to give Obama a try without really knowing anything about the man. I think it matters very much to that voter who Obama really is and what he is covering up.
You can actually attack from BOTH angles. Its not that hard, like walking and chewing gum at the same time.