The Louisiana congressman is smarting after Obama used his first general election ad to endorse Cao’s opponent, Democrat Cedric Richmond. According to Cao’s campaign, he had hoped Obama would endorse him considering all he did for Democrats — like being the only Republican to cast a floor vote for the health care overhaul.

“He didn’t even have the courtesy (to call us)” before running the ad, Cao spokesman Devin Johnson told FoxNews.com. “That hurt the congressman. At least, he wanted that courtesy.”

But Cao says there must be an explanation — Obama must not have known about Richmond’s ethical problems.