Ashford and Graham were better candidates, and ran good campaigns. There's really no magic answer here.
Yep. And Terry and Southerland were terrible candidates and ran bad campaigns. Graham will probably hold on as long as she wants it, but Ashford is probably out in 2016.
I'd reverse that. Ashford will facing much tougher down ballot pressure at the top of the ticket than Graham will, but realistically either both will be re-elected in 2016 or neither will, and it's just to early to tell which story will be true.
They both should be fine in 2016 if they could win in a year this bad. 2018 is another story if a Dem wins the Presidency again.