Twelve states constitute the likely battlegrounds for the 2012 election, based on Gallup’s state-by-state ratings of President Obama’s approval level.

The ratings, which aggregate Gallup polling done from January through June, came out just as Gallup was releasing its latest tracking poll showing Obama’s approval nationwide at 39%, the lowest in his presidency. If Obama’s national approval remains stuck at that level -- or even in the low 40s – then state-by-state assessments probably won’t matter much. Historically, presidents don’t win re-election with that sort of approval rating.

But assuming Obama can move his national numbers back upward, then the 16 states plus the District of Columbia in which he had approval of 50% or better this spring can reasonably be considered his electoral base. They have 215 electoral votes.

At the other end of the scale, there were 22 states where Obama’s approval was below 43% during the spring. Those states, plus Mississippi, where his approval was 45%, but which he stands virtually no chance of carrying, constitute the GOP base, with 168 electoral votes. (Mississippi is a special case because of the racial polarization in its voting; Obama is extremely popular among blacks, who make up almost 40% of the state’s electorate, and very unpopular among whites in the state).

There are 12 states in between. Not all of them will end up being in play – some are likely to prove out of Obama’s reach early on. And although some states may drop off the list, it’s unlikely that many will move onto it. One exception could be New Hampshire – a state that Obama carried in 2008 but in which he is currently quite unpopular. It could become competitive again, depending on the GOP nominee. There are also a few states in Obama’s base that moved sharply toward the GOP in the 2010 election, notably Wisconsin and Minnesota, which the White House still has to worry about.

For now, however, the battleground dozen in the middle of Gallup’s rankings have 155 electoral votes, and to win, Obama would have to capture 55 of those while holding his base. The battlegrounds, which also appear on lists drawn up by strategists in both parties, are three perennial swing states, Florida (29), Ohio (18) and Pennsylvania (20); Iowa (6); three in the South, Virginia (13), North Carolina (15) and Georgia (16); and five states in the West, Oregon (7) plus a grouping in the interior West made up of Nevada (6), Arizona (11), New Mexico (5) and Colorado (9). For those states, Obama would have to depend on a large Latino turnout. The Southern states would require a heavy turnout among blacks plus support from moderate-to-liberal suburban whites.

Gallup’s numbers come from its daily nationwide tracking polls, which surveyed 89,965 adults, age 18 and older, between Jan. 2-June 30.