There are 50 states on The Times’ cool, new “predict a winner” interactive map. But only about 10 of those states really matter for this presidential election, thanks to the electoral college. In a sea of blue and red, these states are gray — and that means up for grabs.

It is one of the oddest features of American democracy. Presidential candidates need only win 270 electoral votes — not the popular vote — to become the leader of the free world.

Electoral votes are awarded state by state, based on congressional representation. So a series of narrow wins in enough states beats huge losses in the others.

INTERACTIVE: Predict a winner

George W. Bush, Benjamin Harrison and Rutherford B. Hayes, for example, ascended to the White House despite the fact that they received fewer popular votes than their opponents. For years, opinion leaders have railed against this quirk of American politics, calling it a historical anachronism and a vestige of slavery.

“The electoral college has elevated the importance of a few swing states — Ohio and Florida, principally — at the expense of the population generally,” the Los Angeles Times editorialized in its wish list of things to fix this year. “It’s long past time to move to a popular-vote system in which the candidate with the most votes wins.”

To tweak Donald Rumsfeld, you have to go to electoral war with the system you’ve got. From now until November, expect to hear a lot about Ohio, Florida, Virginia, Iowa and Colorado, the states that could determine whether Barack Obama gets a second term. The Los Angeles Times is publishing a series of stories labeled “The Battlegrounds.” The Wall Street Journal has dubbed similar coverage “Swing Nation.”

Obama, Mitt Romney and their surrogates will be slugging it out in these battlegrounds, kissing babies and eating rubber chicken in places such as Ames, Iowa and Dayton, Ohio. Much of Obama’s travels as president has been to these swing states. Air Force One’s flight plans have included Ohio at least 20 times since Obama entered the White House.

My colleague Paul West is one of the best at keeping score of the electoral map. He reported recently that Romney has to win Virginia and Ohio to have any realistic chance at securing victory. Obama is almost certain to be reelected, West says, if he wins either one. He won both in 2008.

If he loses Ohio or Virginia, Obama will need to win Pennsylvania and smaller battleground states — Colorado, Iowa, New Hampshire and Nevada — to get to 270.

Writing in the Wall Street Journal, former Bush adviser Karl Rove did his own electoral math recently and calculated — surprise! — that the odds favor Romney.

Romney would need to repeat all of John McCain’s wins in the 2008 election, wrest Indiana, North Carolina and Virginia from Obama, and secure Ohio and Florida. That gets Romney to 266 votes compared with 272 for Obama. So Romney needs to win one other state to best the president.

You can follow the electoral back-and-forth on Politics Now.

Just don’t try making sense of the electoral college. Here’s the way one American articulated the problem: “The present rule of voting for president ... is so great a departure from the Republican principle of numerical equality ... and is so pregnant also with a mischievous tendency in practice, that an amendment of the Constitution on this point is justly called for by all its considerate and best friends.”

The speaker’s name was Madison, as in James Madison.

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Maharaj is Editor of The Times.

davan.maharaj@latimes.com