Maybe Robert De Niro didn't know. Or maybe he forgot.

But when the superstar actor joked at a New York Obama campaign fundraiser Monday evening which Michelle Obama attended about the country not being ready for a white first lady, he got into dangerous territory for President Obama.

According to an Obama campaign pool report, De Niro deadpanned:

"Callista Gingrich. Karen Santorum. Ann Romney. Now do you really think our country is ready for a white first lady?"

The well-heeled audience laughed uproariously. Someone shouted "No!"

De Niro then added, "Too soon, right?"

The Obama campaign distanced itself from De Niro's joke Tuesday. "We believe the joke was inappropriate," said Olivia Alair, Mrs. Obama's campaign press secretary.

Meanwhile, Newt Gingrich, the Republican presidential candidate, pounced:

"What De Niro said last night was inexcusable and the president should apologize for him. It was at an Obama fundraiser, it is exactly wrong, it divides the country..."

While De Niro was clearly being mock ironic by recalling the kind of comments that many whites made about blacks within living memory, he ran afoul of the unwritten rule Obama and his tight knit team of advisers have operated under going back to his 2008 campaign. Anything that reinforces racial divisions or focuses attention on the president's race should be avoided.

Obama succeeded in winning office, in part, because he didn't run as an African American politician. Instead, he ran as a politician who happened to be African American.

Some might not see the difference in that but it's significant. The former places the stress on group identity and would have risked making him seem like too much of "the other" to too many Americans than he already seemed.

The latter emphasized his personal story, parts of which many Americans could identify with.

It doesn't take a Harvard-trained social scientist to figure out that in a society that has a way to go before it is post-racial, if indeed it ever gets there, Obama needed to walk the tricky line of downplaying race where ever possible without doing it to such a degree that he hurt himself in the eyes of black voters.

As he campaigned, so he has mostly governed. He's a president who happens to be African American, the first to occupy that office.

Not that it's been easy to avoid being pulled into the racial vortex. He interjected himself into the controversy that ensued after Cambridge, Mass. Police Sgt. James Crowley, who is white, handcuffed the Harvard scholar-celebrity Professor Henry Louis Gates, who is black, in the historian's own home.

Then there was his Agriculture secretary's summary firing of Shirley Sherrod after the African American former Agriculture Department official was victimized by the release of a selectively edited video by the late conservative blogger Andrew Breitbart.

The abridged video made it appear Sherrod boasted to a black audience of practicing reverse discrimination when she had done nothing of the kind.

But as reporters who have written about the 2008 campaign and Obama presidency have noted, the nation's sorry racial history and continued difficulties on the issue are just a political minefield the president would rather not have to walk through if he doesn't have to.

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