It could be portrayed as a flip-flop, but only by Republicans. McCaskill has to tread a fine line on it - I think she would be pro stem cell research but if she ends up bashing him for agreeing with her then it makes her look bad.
I would have thought that this is what pushed his numbers up slightly as he gets press attention and discusses issues, resulting in a favourable atmosphere for him.
I think that McCaskill should pull it out in the end. The poll notes that more Missourians approve of her than Talent and more Missourians disapprove of Talent than her. Apart from the money factor, which is weighted against her, she is running in a swing-state in a good year for her party against an empty-suit of a politician who has got no credit for any legislation or activity in MO. Furthermore, she is familiar and well positioned in the eyes of the voters: 48% of them voted for her in 2004.
