In Reno, Nevada's Washoe County, Obama leads McCain by a 46-45 percent margin, with six percent undecided. Obama posts a wider 50-44 percent lead with five percent undecided in Raleigh, North Carolina's Wake County, and another 6-point lead in Hillsborough County, Fla., where Tampa is located. There, he edges McCain 47-41 percent, with 11 percent undecided.
Among the four counties tested, McCain leads in only one: Jefferson County, Colo., a populous Denver suburb. McCain is ahead there by a margin of 45-43 percent, with eight percent undecided.
At first glance, these Politico/InsiderAdvantage numbers might not look so troubling for McCain, who trailed Obama by 10 points in an ABC/Washington Post national survey, released Monday.
But these four counties are crucial battlegrounds in four of the most competitive states in the presidential race. In recent years, the Republican path to the White House has run through these areas.
In 2004, President Bush won Washoe County, Nevada's second-most populous county, by a four-point margin over Massachusetts Sen. John F. Kerry. This year, when Obama is expected to run up a big vote lead in Las Vegas' Clark County, McCain is unlikely to be able to afford a loss in Washoe.
Colorado's Jefferson County supported GOP presidential candidates by an average of almost 18 points between 1976 and 2004. While it hasn't supported a Democrat since 1964, Jeffco has become much more politically marginal in recent years—in 2004, Bush beat Kerry there, 52-47 percent. It was no coincidence that McCain running mate Sarah Palin made her first solo campaign appearance after the Republican National Convention in Jefferson.
Tampa's Hillsborough County, which Bush carried 53-46 percent in 2004, and Raleigh's Wake County, which Bush won 51-49 percent in 2004, have been more evenly divided historically. With substantial minority populations and, in Wake County's case, a more affluent and educated electorate, they began this campaign as less friendly territory for McCain.
Still, Bush carried both counties in his two presidential bids and Obama's strong performances in these areas represent a troubling sign for the McCain campaign.
InsiderAdvantage pollster Matt Towery, who conducted the survey, said McCain's lagging numbers could be largely attributed to weak showings among independents and male voters.
"When you begin to see McCain fall apart in these states, it's because that male split becomes less and less," said Towery, who emphasized that McCain would have to perform well among men to make up for Obama's strong advantage with women voters.
Nevada's Washoe County features a dramatic gender gap, with women favoring Obama, 54-36 percent, and men choosing McCain, 55-38 percent.
But in Florida's Hillsborough County, Obama not only won 49 percent of women voters, to McCain's 43 percent, but he captured a plurality of male voters, beating McCain by a 45-39 percent margin.
In North Carolina's Wake County, the state's second-most populous after Charlotte's Mecklenburg County, McCain came closer to Obama's share of the female vote, with the Democrat leading by just over four points. But among men, Obama led McCain, 51-43 percent - an untenable split for the Republican nominee.
Hillsborough County's trend toward Obama mirrors the overall GOP slippage in the Sunshine State in recent polls, as Florida Hispanics, a demographic once dominated by conservative Cuban-Americans, flirt with the Democratic Party.
By a 60-40 percent margin, Hillsborough County Hispanics support Obama over McCain. That's a smaller margin than Obama's national margin among Hispanics. But given the historically Republican tiltof Florida's Hispanic population it's a margin that should worry McCain, Towery said.
"I would say a majority of the Hispanic vote in Florida is not the anti-Castro, Cuban-American vote," said Towery, citing both Florida's growing Puerto Rican and Mexican-American populations, as well as the increased presence of younger, more liberal Cuban-Americans as reasons for this trend.
Exit polls in 2004 showed Bush defeating Kerry among Florida Hispanics, 56-44 percent.
In North Carolina, the growth of college-educated, high-income voting areas has helped move the state toward the Democratic column. The state's large African-American population gives Obama an extra demographic boost that could make the difference on Election Day.
"Wake was very marginally Republican in 2004," Towery said. "[Obama] carried it almost 2-1 over Hillary Clinton, and that is because it's located in the Research Triangle and it has basically the sort of demographics you would expect to see for the profile that Obama does well in."
Even outside the Research Triangle, though, North Carolina has drifted toward the Democrats this year, with Obama establishing a narrow lead in most statewide polling and Democratic Senate candidate Kay Hagan, a state legislator, locked in a tight race with GOP Sen. Elizabeth Dole, who is seeking reelection to a second term.
Where the other Politico/InsiderAdvantage county-level polls showed similar results to statewide polling, only in Jefferson County did the result - a razor-thin edge for McCain - clash with the results of recent state-level surveys. An InsiderAdvantage poll released last week showed Obama ahead in Colorado, 51-45 percent.
McCain's lead in Jefferson, Towery said, was in part an expression of the county's Republican lean. Forty percent of Jefferson County voters identify as Republicans, with just 28 percent calling themselves Democrats.
But even in spite of this identification edge, and the county's Republican voting history, Obama is competitive there thanks to strong support among independents, who favor him by a 48-30 percent margin.
Among the bellwether counties surveyed, there is still some promise for McCain. While Obama is leading or tied in these places, his strength is based on support among groups that would typically vote Republican - and who might be easier for McCain to take back. In theory, McCain should have an easier time winning over male voters or white independents than women voters or Hispanics.
"If somehow John McCain should pull something off that turns things around," Towery said, or if the markets find steadier footing, "then there is the possibility that McCain's numbers could start to tick up."
For now, though, this snapshot of four of the country's most competitive counties shows Obama peeling off voters who once made these areas reliably Republican in presidential elections and exploiting political and demographic trends that were already sending these counties in his direction.
The Politico/InsiderAdvantage telephone surveys in Jefferson County and Hillsborough County were conducted Oct. 12. The Hillsborough survey included 638 likely voters, with a margin of error of plus or minus 3.8 percent.The Jefferson survey included 408 likely voters, with a margin of error of plus or minus 5 percent.
The Politico/InsiderAdvantage telephone surveys in Wake County and Washoe County were conducted Oct. 9. The Wake survey included 646 likely voters, with a margin of error of plus or minus 3.7 percent. The Washoe survey included 586 likely voters, with a margin of error of plus or minus 4 percent.