As Michael Barone crunches numbers for the November election, he has focused on a presidential strategy for countering challenger Mitt Romney. That strategy focuses on North Carolina, Ohio, and Florida, as Barone details in his latest column.

In three states, Obama is currently polling only 3 or 4 percent below his actual vote in 2008 — North Carolina, Florida and Ohio. Probably not coincidentally, these were three of the four states where his winning percentages were lowest (in the fourth, Indiana, he seems far behind this year).

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 roughly 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.