Pundits from Bob Novak to Paul Krugman have argued that Sen. Barack Obama is underperforming because his lead of about 5 to 7 points lags behind how a "generic" Democrat fares in congressional election polls, leads ranging from 10 to 18 points.

But looking at the leads can be misleading.

Look at the levels of support in generic congressional ballots:

AP-Ipsos
Dem: 53%
GOP: 35%

Research 2000
Dem: 51%
GOP: 37%

NBC/WSJ
Dem: 49%
GOP: 36%

Pew
Dem: 52%
GOP: 37%

ABC/W. Post
Dem: 53%
GOP: 38%

CNN
Dem: 54%
GOP: 44%

The generic Democratic candidate generally polls in the lower 50s, the generic Republican generally polls in the upper 30s, with a bunch of undecideds left over.

I would not expect the generic Democrat to pick up much more from that pool of undecideds, which probably contain a lot of disaffected conservatives and conservative-leaning independents sitting on their hands. (Democrats won 53.6% of the vote in 2006 when they took back the House, already a pretty strong number historically.)

Obama performs a little bit under that. The most recent polls from CNN, Pew and AP-Ipsos have him at 51%, 47% and 47%.

(A Zogby poll has Obama at 41%, slightly trailing McCain by 1, but that would appear to be an outlier, and one where McCain still languishes at 42%.)

But the difference between Obama's high 40s and generic Dem's low 50s is not as stark a gap as the contrast between a 6 point presidential lead to a (probably overstated) 15-point generic Dem congressional lead would appear to be.

Furthermore, does even that small gap speak to any flaws specific to Obama?

Nate Silver argues that Dem voter loyalty to presidential candidates has always been soft.

As the front-runner, Obama faces a daily barrage of attacks that a generic Democratic does not, swing doubt that keeps some folks on the fence. Anyone else in his place would also likely trail a generic placeholder by at least a similar amount.

And McCain is a candidate who has long polled well with independents, allowing him to outperform a generic Republican -- also something that would be the case regardless of Dem nominee.

Meanwhile, McCain still can't crack 45% in nearly every poll, and he's caught in a bind: trying to consolidate the conservative base and appeal to independents at the same time.

Childish attacks against Obama can get McCain out of the 30s and into the 40s by consolidating conservatives, but they can't get him the independents needed to get in spitting distance of 50%.

The bottom line is as it was: Obama is in a good position, but there remains a pool of undecideds around 10% of the electorate -- many of whom are disengaged voters that won't choose until late -- that can't be taken for granted.