Barack Obama has seen his support erode over the last two months, and what had been a comfortable lead has disappeared into a virtual tie.  John McCain has begun to rally reluctant Republicans and has made inroads among working-class voters.  The biggest factor, according to Pew Research?  Leadership:

With less than two weeks to go before the start of the presidential nominating conventions, Barack Obama’s lead over John McCain has disappeared. Pew’s latest survey finds 46% of registered voters saying they favor or lean to the putative Democratic candidate, while 43% back his likely Republican rival. In late June, Obama held a comfortable 48%-to-40% margin over McCain, which narrowed in mid-July to 47% to 42%.

Two factors appear to be at play in shifting voter sentiment. First, McCain is garnering more support from his base – including Republicans and white evangelical Protestants – than he was in June, and he also has steadily gained backing from white working class voters over this period. Secondly and more generally, the Arizona senator has made gains on his leadership image. An even greater percentage of voters than in June now see McCain as the candidate who would use the best judgment in a crisis, and an increasing percentage see him as the candidate who can get things done.

And how has Obama fared? Poorly:

Conversely, Obama has made little progress in increasing his support among core Democrats since June – currently 83% favor him compared with 87% of Republicans who back McCain. The likely Democratic nominee is still getting relatively modest support from Hillary Clinton’s former supporters: 72% of them support Obama, compared with the 88% support level that McCain receives from backers of his formal GOP rivals. Obama’s strong points with voters are in being seen as the candidate with new ideas and as someone who connects well with ordinary people.

Pew found that a nine-point edge for McCain on crisis leadership in June has increased to 15 points in August. The polling period included the first couple of days in the Caucasus conflict, but the fallout from that would almost certainly come afterward. McCain’s experience and years of accurate analysis on Russian intentions got more play on Monday of this week, the day after the polling ended.

McCain made gains in two other areas as well.  Obama’s conceit of independence has failed to resonate with voters; McCain now leads on “willing to take unpopular stands” by 11 points, as opposed to three in June.  He erased an Obama lead on the ability to accomplish things, going from a six-point deficit to a two-point lead.  Obama leads on passion, however, with 27% of his 46% strongly supporting him (which is down a point) to only 17% of McCain’s 43% in strong support.  McCain went up three points in this category since June, though.

McCain still has a significant gap among women, which went down only a point in two months.  However, McCain has taken the lead among men from Obama, who led 45-44 in June and now trails 49-41.  Oddly, McCain picked up two points among black voters, but picked up most of his gains among working- and middle-class voters, and those voters with high-school education or less.

With two weeks before the convention, Obama needs a momentum reversal, and he needs it quickly.