US elections are not head-to-head popularity contests in which the candidate with the most votes nationwide always wins — but comprise distinct state races requiring piles of cash and on-the-ground networks.

In 2008, President Barack Obama expanded the Democratic map and won nine states that voted for Republican George W. Bush in 2004.

The 2012 contest will likely depend on those states: Iowa, Ohio, Virginia, North Carolina, Indiana, Florida, Colorado, New Mexico and Nevada, and several other possible battlegrounds: Pennsylvania, Indiana, Wisconsin and Michigan.

When “safe” states are totted up, Obama looks assured of around 197 of the 270 electoral votes he needs to win, while the Republican nominee can count on around 183 — setting up a desperate fight for the remaining 158.

Each state is allocated a proportion of votes in the Electoral College which is indirectly calculated depending on its individual population.

A candidate needs 270 electoral votes to win the White House, so must build a coalition of big, small, rural or urban states to reach the magic number.

The key in 2012 will be how well each party turns out their core support — Republicans are seen as more energized than Obama’s Democrats — and how well they connect with crucial independent swing voters.

A year from the election, polling is patchy in some states and based on hypothetical matchups between Obama and potential Republican foes.

But the 2012 election looks set to be a cliffhanger and no candidate is expected to approach the 365 electoral votes Obama amassed in 2008.

“Our presidential forecast models don’t kick in for another 10 months, but right now they are showing that the presidential race is a toss-up,” said political science professor Matt Dickinson of Middlebury College.

It is clear that Obama faces a troublesome political environment: in a CBS/New York Times survey last month, only 21 percent believed the country was heading in the right direction.

Obama’s approval rating at 43 percent in the latest Gallup daily tracking poll, is depressed, but within striking distance of a spot in the high 40s a president needs to have a decent chance of a second term.

———— Economic blight to shrink Obama’s map ————

The poor economy and high unemployment seem certain to shrink the president’s electoral map.

In a hypothetical matchup with Republican frontrunner Mitt Romney, he is at grave risk of losing Virginia, North Carolina, Indiana and Florida — all of which he won in 2008.

In such a scenario, Obama would be reliant on locking in industrial midwestern states like Ohio, Michigan and Pennsylvania, and dominating western battlegrounds like Colorado, Nevada or New Mexico.

Obama campaign aides also dream of putting an unlikely squeeze on the Republican nominee in Arizona, Montana or Georgia.

But if the Republican wins both Ohio and Florida — bellwethers with 18 and 29 electoral votes, Obama’s route to victory may shrivel.

The last time Ohio did not vote for the eventual winner of the White House was 1960 and Florida was the epicenter of the 2000 recount debacle which ended with George W. Bush being anointed by the US Supreme Court.

Nationwide, Obama will seek to reunify his 2008 coalition of young voters, African Americans, the educated middle classes and Hispanics while seeking to motivate core Democrats in vital midwestern battlegrounds.

But he faces a tough task in winning over vital independent voters who often sway US elections but soured on his economic management after 2008, and trails badly among blue collar whites.

In a poll in October, 54 percent of independents surveyed by the Pew Research Center backed Romney while 41 percent chose the president.

Republicans are concerned that their coalition of mainly white voters is thinning as America becomes more racially diverse, and need to court minorities and the educated middle class.