This race is winnable for the Republicans if they play their cards right. Evan Bayh strikes me as a low energy politician from another era (when many deep red states had safe Democratic Senators), who has never been significantly challenged since perhaps his days as Governor. His polls numbers are a reflection of the name and a longing/nostalgia for a different era. Introducing Bayh to the new reality, will bring his poll numbers down to earth.
There is no denying that Bayh is a Clintonista. The very fact that he is willing to run now should illustrate that fact. My recommendation would be to tie him to Clinton and hammer him as a rubber stamp. Bring up Obamacare, immigration, even trade if necessary. Most likely Indiana votes for Trump and even if it don't, it will be with extreme reluctance and misgivings about Clinton and thus plenty of appetite for someone who will stand up and hold her accountable.
I'm not so sure this is a smart move, but it is definitely doable, especially given Bayh's vote for Obamacare. I don't think you're going to run ahead of Trump by tying your opponent to his opponent.