I am not sure you are saying something different to me.
You agree that people on the left are not down on Obama at the moment. I was trying to put a little measurement into the statement that there's a massive discontent with Obama. It's mainly among Republicans, and if Trump's candidacy is the principal enthusiastic expression of it, it can easily be ignored.
In the last couple of elections PPP has been a fairly reliable polling organisation. Scroll down to the bottom to see Obama's figures. Not surprisingly, discontent is pretty much just a partisan number.
http://elections.huffingtonpost.com/pollster/polls/ppp-d-22415