The idea behind a Trump candidacy was that Trump would win over a Democratic crossover. To win the Presidency, any Republican must cut significantly into the Obama coalition. So far no Republican does that.
President Obama is not a failure. He is clearly far better than his awful predecessor; any Republican who offers nostalgia for the George W. Bush era will find himself facing a barrage of counter-nostalgia. Basically, "It's been tried, and proved a failure". Approval polls of Barack Obama are consistently in the middle-to-high 40s, which is enough to win re-election.
Republicans disapprove of Barack Obama the person (which may have a racist component); Democrats are disappointed that President Obama didn't get what he promised -- for which they blame Republicans. Democrats still want the Obama agenda and may want to go beyond it. So what do Republicans have to offer? Not much for Democrats.
I think that Kasich does that. He often talks about coming together, especially both parties.
