Nelson, Ben NE; Nelson, Bill FL and in AK are prime. as is Byrd.
Dewine and Talent will have compition.
I think if the Dems remain the party of 'No' only without viable alternative ideas and the above Dems stand with the NE liberals, they could have problems. I think thinkgs, based on that list, could remain the same. Byrd should retire IMO. WVa has been a hard nut to crack though.
it will be hard to beat ben nelson in nebraska. although a democrat, he is much more conservative than chuck hagel. it will be a tough contest if current governor johanns goes after nelson's seat; not unwinnable, but a tough prize to grab.