9 Swing States are Main Focus of Ad Blitz HENDERSON, Nev. - The presidential campaigns and their allies are zeroing in mainly on nine swing states, bombarding them with commercials in the earliest concentration of advertising in modern politics. With so many resources focused on persuading an ever-shrinking pool of swing voters like those here in Nevada, the 2012 election is likely to go down in history as the one in which the most money was spent reaching the fewest people. Much of the heaviest spending has not been in big cities with large and expensive media markets, but in small and medium-size metropolitan areas in states with little individual weight in the Electoral College: Cedar Rapids and Des Moines in Iowa (6 votes); Colorado Springs and Grand Junction in Colorado (9 votes); Norfolk and Richmond in Virginia (13 votes). Since the beginning of April, four-fifths of the ads that favored or opposed a presidential candidate have been in television markets of modest size. Nowhere is this more apparent than in southern Nevada, where a costly and contentious fight is playing out for six electoral votes. Already, ads about President Obama or Mitt Romney have been run nearly 6,000 times in and around Las Vegas since April 11, more than in any other media market in the country during that period, according to the Kantar Media Campaign Media Analysis Group. And the $5 million spent by both sides during that eight-week stretch translates into the highest rate of spending per electoral vote anywhere by far. Underscoring the state's importance this year, Mr. Obama campaigned in Las Vegas on Thursday; Mr. Romney visited last week for a rally and a fund-raiser. All this effort is to reach just 1.4 million registered voters, a sign of how tight this election is expected to be. And it points to how the country's growing partisan divide has redrawn the political geography, with fewer states than ever not firmly designated "red" or "blue." A study released this week by the Pew Research Center found that the differences between Republicans and Democrats on a wide range of questions - like whether someone believes in God and what role the government should have in helping the poor - have never been starker in the 25 years since Pew began the survey. These divisions play out on television sets across the sprawling desert developments here, where political ads start with the 4 a.m. newscasts. They appear alongside commercials for bankruptcy lawyers and the "sizzlin" million-dollar giveaway" at a supermarket chain, reminders of how the economic recovery has skipped over much of Nevada. In one ad, a minute-long spot from the Karl Rove-backed group Crossroads GPS, a litany of Mr. Obama's "broken promises" is punctuated by the sound of shattering glass. Another ad uses a stopwatch to drive home the point that the national debt increases $1.4 million every second. It lays the blame squarely at the president's feet ("borrowing from China for his spending," it says) despite sharp deficit growth under George W. Bush. The Obama campaign's presence is equally strong on the air, and it grew even heavier this week with a new $10 million ad campaign in Nevada and eight other states. The latest ad claims that as governor of Massachusetts, Mr. Romney had "one of the worst economic records in the country." "It is unusual that so few states are in play from an advertising standpoint," said Will Feltus, senior vice president of National Media, which researches and plans advertising placement. He said that the sheer amount of money in play this year is a factor. And because neither candidate is accepting public financing, which would put limits on how his campaign spends, the campaigns can be more strategic about how they advertise. "I think campaigns this year are marshaling their resources more carefully," he said. Given the volatility of the electorate, the map could easily expand or contract from the current nine - Colorado, Florida, Iowa, North Carolina, New Hampshire, Nevada, Ohio, Pennsylvania and Virginia - in the weeks and months ahead. And advertising is only the most tangible sign of which states are competitive. There are other factors like voter registration and organization that play important roles. But no recent general election advertising strategy has covered so little ground so early. In the spring of 2000, George W. Bush and Al Gore fought an air war in close to 20 states. In early 2004, there were the "Swing Seventeen." And in 2008, the Obama campaign included 18 states in its June advertising offensive, its first of the general election.