At last count by the Washington Post's estimate, the Democrats and Republicans have together spent an unprecedented $600 million on television advertising in the so-called 12 swing states, especially Ohio, Florida and Virginia, states that might ultimately determine the U.S. presidential election on Nov. 6. And the money will certainly keep on flowing for the duration of the campaign.
Swing or battleground states seem mysterious. Why Ohio, Florida and Virginia, for example, rather than California, New York and Texas? What demographic and historical factors account for this seemingly bizarre situation that a dozen of the 50 states possess this power to decide who becomes the next American commander-in-chief?
It was in the 1888 American election that political pundits first identified swing states. In that contest, between Democrat president Grover Cleveland and his Republican opponent Benjamin Harrison, the vote came down to the election in four unpredictable states: Connecticut, New York, New Jersey and Indiana. Harrison's narrow victory in Indiana and New York proved the difference in making him the president.
To understand the curious swing-state phenomenon, you have to go back even further to the late eighteenth century.
The U.S. might be the bulwark of democracy in the world, but its constitution was designed in the 1780s with several anti-democratic features. In fact, many of the "framers," as the delegates to the constitutional convention of 1786-87 are deferentially called, were frightened by the idea common people might decide who runs the country.
"The people should have as little to do as may be about the government," declared Roger Sherman of Connecticut.
Alexander Hamilton, who later served as the first secretary of the treasury under George Washington, concurred. "The people are turbulent and changing," he said. "They seldom judge or determine right."
As such, the framers opted for an indirect system to choose the president through that most unique American political invention, the electoral college.
This placed the final decision on the presidential election in the hands of state representatives known as electors -- supposedly knowledgeable and responsible officials, but in reality for many years merely wealthy and influential white men who were political insiders.
The number of electoral votes in the college each state (and the District of Columbia) is allocated is determined by population; hence, California has the most, 55, while New Hampshire has only three.
Over the years, the independence of the electors has been removed and in almost every state their final determination done about six weeks after the November election is governed by the popular vote.
All a candidate has to do, therefore, is to win a state, even by the smallest of margins, and he or she wins all of the state's electoral votes. There are a total of 538 electoral votes to be won, so a candidate has to amass 270 electoral votes to claim the presidential crown.
In 2008, Barack Obama won 373 electoral votes to Republican nominee John McCain's 173.
What this means in practical terms during a campaign is that both candidates will spend much more of their time and resources in heavily populated states with significant electoral votes and particularly in heavily populated states that for one reason or another have a historically close voting pattern, such as Florida and Ohio.
So-called safe states such as New York (29 electoral votes), which has voted Democrat since 1988 -- and all but six times since 1932 -- and Texas (38 electoral votes), which has gone Republican in every election since 1980 -- and all but four since 1952 -- receive less attention. It is all a question of playing the odds.
The electoral college system has another wrinkle. A candidate can win the overall popular vote, but still lose, as Al Gore did in 2000 when he received 543,895 more votes than George W. Bush, but lost the election because Bush won 271 electoral votes to Gore's 266.
The difference in one of the most contentious disputes in U.S. history came down to which candidate won Florida's popular vote. After several recounts (remember the infamous hanging "chads" on the contested ballots) and a month of legal fighting, the courts determined Bush had won by a mere 537 votes -- 2,912,790 to 2,912,253. Yet that was sufficient for Bush to take all of Florida's 25 (now 29) electoral votes and claim the presidency.
The close vote in 2000 designated Florida as a key swing state, though it was not always so. For much of its history, Florida had been part of the "solid South" and reliably voted Democrat, until a realignment of the two parties occurred in 1952 when it and other southern states opted for the Republicans.
Between 1952 and 2008 in 15 elections, the Republicans captured Florida (though not always easily) in all but four contests -- 1964, 1976, 1996 and 2008.
Similarly since 1970s, the Republicans and Democrats have battled for Ohio's 18 electoral votes.
And for good reason. Since the 1944 election, the only time a candidate did not win Ohio and still became president was in 1960, when a slim majority of Ohioans voted for Richard Nixon instead of the winner, John F. Kennedy.
In 2004, George W. Bush won Ohio with only two per cent more of the vote than John Kerry and in 2008, Obama beat McCain by five per cent. In both elections, Ohio's electoral votes were highly significant in each candidate's victory.
As in 1888, it all comes down to a mixture of socio-economic factors and population diversity. Both Ohio and Florida, for example, have areas with a high concentration of minorities (especially ever-increasing Hispanic populations), which tend to vote Democrat, as well as a high concentration of wealthy white Americans, who traditionally have voted Republican. Another random element is white women who usually, but not always, favour the more liberal Democrats.
In Florida, a popular destination for Cubans, Latinos and retirees, there is "a constant influx of new residents (that) can make a difference from one election cycle to the next," Brendan Farrington of the Associated Press says. Four years ago, 8.4 million Floridians voted and Obama only defeated McCain by 236,000 votes.
Stanford University historian Jack Rakove argues there is "nothing special" about the swing states. "Their competitiveness," he says, "is just a demographic accident."
True enough, but keep this in mind: All things being equal, if Obama holds the safe Democratic states and wins Ohio, he will only be 15 electoral votes shy of the 270 majority. If, on the other hand, Romney takes Ohio and Florida, along with a few other key swing states, it could be enough for him to win it all.
In short, in the next few weeks, if you want to get a glimpse of either presidential candidate, your best bet to run into them would be in Cleveland, Cincinnati, Miami or Tampa.
Now&Then is a column in which historian Allan Levine puts the events of today in historical context.