In 2008, the Obama campaign was able to spot openings in previously safe Republican states and use its money advantage to carry them. It looks like the 2012 Obama campaign has been concentrating its money, as well as appearances by the president and cabinet members, in these three states with 62 electoral votes in the hope that they will be a firewall preventing Romney from reaching the 270-vote majority.
But it looks like the Obama forces won't be able to heavily outspend the Republicans from now on. And the risk is that if opinion moves against them by a few more points in these firewall states, it will also do so in other states that weren't necessarily on the target list in 2008 but are now.
These include the manufacturing states of Michigan and Indiana, with 27 electoral votes, where Obama's current poll numbers are nearly or more than 10 percent behind his 2008 showing, and Missouri, with 10 electoral votes, which he nearly carried in 2008 but which now looks out of reach.
They also include six states with 46 electoral votes that have very low percentages of black voters -- Colorado, Iowa, Minnesota, New Hampshire, Oregon and Wisconsin. Obama carried all of these handily, but his current polling is seven to nine points behind his 2008 percentage.
And they include Virginia, with 13 electoral votes, the one state that matched the national percentages for Obama and John McCain and where Obama's current polling lead is 47 percent to 44 percent.
All of these 10 states, with 96 electoral votes, cast more votes for Republicans than Democrats in 2010 House elections. That was true also in Pennsylvania and Nevada, which together have 26 electoral votes.
Poll numbers are imprecise and subject of course to change. My point is that the list of target states has changed and gotten larger -- and could change and grow even more.