Much of the day I've been reading Daily Kos on my phone (since I've been at work) and Jed's coverage of the Convention has focused on "We Built That" chant/retort/refrain by Republican speakers. Here's my thought about it.
While Jed noted on the front page the "We Built That" was a confirmation of Obama's main point that government pooling of money for collective good often yields good for society like roads and bridges I view the whole scenario differently.
It's horrible to say, but for many Republicans a black man said "you didn't build that" and the overwhelmingly white Republican party has retorted "we built that". The point of individual vs. collective construction of buildings/businesses/assets seems to have dripped away and we're left with a basic premise about Obama, that he's fundamentally un-American, calling into question the collective body of work created by "white America" who have held power and wealth since America began.
In short (I think) that Republicans are saying "we" [white people] built America". That's part of a thought. The other part is that "you [other people] didn't build America." I think the reason this non-issue has been kept alive so long is that Obama said one specific idea and white people heard a completely different thing. Consequently, white Republicans, who want "to take America back" and its institutions as their birth right, respond "We built that". "That" being America, not just it's roads and bridges but the wealth and army and the entire idea of American exceptionalism.
~Just a thought from my brain.
8:29 PM PT: I hate to think that people are still racist and I think for many people it's a subconscious perception that someone they consider un-American is questioning of their patriotism and citizenship even if Obama is also a black man.