...are there enough rank-and-file Republicans whispering their support at Obama rallies to actually make a difference on Election Day?

I discovered from examination the last 18 months of head-to-head general election polls, the answer seems to be "no." In fact, John McCain's share of the Democratic vote has typically--and surprisingly--been larger than Obama's share of the Republican vote. In other words, it's not that the Rev. Jeremiah Wright scared the Obamacan masses off, as some pundits have theorized--it's that they never existed (in any unprecedented way) to begin with. In December 2006--before the unfamiliar Illinois senator had officially announced his candidacy--McCain attracted 25 support among Dems versus Obama's eight percent among Repubs, according to a FOX News poll**. Those numbers tightened over the next few months of polling by various firms, but Obama never established a sustained lead. A February 2007 Quinnipiac survey showed McCain with 17 percent crossover support, for example, versus nine percent for Obama; in a June 2007 sounding by the same outlet, McCain still led 15 percent to 11. During primary season--between December 2007 and April 2008--McCain's Democratic number typically hovered between 18 and 22. Obama, meanwhile, never climbed higher than 13 percent.

Much of this gap can be attributed to the primary clash with Clinton, whose supporters often said they preferred McCain to Obama in head-to-head polls taken before the final Democratic contests on June 3. But even though McCain's support among Dems declined after Hillary bowed out--a natural result of Democratic unity--Obama's Republican backing didn't budge. Today, Republicans for Obama and Democrats for McCain effectively cancel each other out. The latest numbers from CBS News show Obama at 11 percent crossover support and McCain at 10 (and tied among Independents); FOX News puts the pair at six percent and seven percent, respectively--a result that closely matches where George W. Bush (nine percent crossover) and John Kerry (seven percent crossover) stood at this point in 2004. That also deadlock mirrors 2000, when George W. Bush won over 11 percent of Democratic voters and Al Gore poached eight percent of Republicans--and it means that neither Obama nor McCain, both of whom have repeatedly boasted of their "strong record[s] of bringing people together from the left and the right to solve problems," can currently rely crossover voters to carry them to victory.

I'm not saying Obamacans don't exist. They do. It's just that there's little statistical evidence to support the claim that the number of Republicans who favor this year's Democrat is substantially larger than the number of Republicans who favored his predecessors.

With polls showing Obama dominating among those under 40 and running even among middle-aged voters, Republican John McCain's lead among those 65 and older is the main reason he remains close overall. His margin is largest among older white voters without a college education, accounting for much of Obama's problem with the white working class.

Obama has tried to compensate by proposing a tax cut for seniors, which was criticized by economists. But as Rutherford's comments suggest and surveys show, Obama's challenge goes deeper than a new proposal or two -- an approach that worked for Clinton against George H.W. Bush and Robert J. Dole.