Today we start with a quiz. Two politicians, one black and one white, have a disagreement on an issue. One airs an opinion, and the other responds with a racial insult. What will happen next?

A) The politician who used the racial insult will be roundly and widely denounced and forced to resign from office.

B) Nothing.

The answer is: It depends. It's impossible to determine the correct answer without knowing whether the epithet came from the white politician or the black politician. In a society that treats racism, correctly, as a grave offense, it shouldn't really matter. But apparently it does.

If you don't believe me, consider the case of Illinois' U.S. Rep. Bobby Rush, a black Democrat, and Sen. Mark Kirk, a white Republican. Kirk has been urging law enforcement agencies to destroy Chicago's biggest gang by arresting its members—all 18,000 of them.

It's easy to spot possible flaws in this proposal. There is no jail in Chicago big enough to hold all those arrestees. There are not enough police in the city to carry out such a massive detention. There is no reliable membership list to make sure that only the guilty get picked up.

It would cost a lot of money—Kirk wants the federal government to provide $30 million for the task. It would divert cops from just about everything else they normally do.

Some of these defects obviously occurred to Rush, who found no merit in the idea. "It's a sensational, headline-grabbing, empty, simplistic, unworkable approach," he told the Chicago Sun-Times. All fair points, made in perfectly acceptable language.

But Rush wasn't content to stop there. Kirk's proposal, he declared, is "an upper-middle-class, elitist white boy solution to a problem he knows nothing about."

After reconsidering, Rush issued a more temperate statement, expressing his sincere regret that Kirk's "current plan does not include the option to create jobs, provide affordable and safe housing, quality health care and improve schools in urban areas." But on the topic of the senator's pale complexion, Rush saw no need to amend or retract his words or apologize for them. (His spokesperson did not return my calls asking for comment.)

Nor did the Sun-Times treat the comment as scandalous. Kirk's spokesman ignored it in a mild statement, saying, "The senator will continue to work with Sen. Durbin, Mayor Emanuel, law enforcement and the entire congressional delegation to keep Illinois families safe."

But consider how things would have gone if it had been Kirk instead of Rush who made an insulting racial comment—not even the N word, but something less offensive.

I won't attempt to come up with a hypothetical equivalent, since ethnic slurs are really not my strong suit. But it's fair to assume that if Kirk had used any sort of pejorative racial term to refer to Rush, he would have soon been renouncing it in a desperate attempt to save his political career.

It's true that Kirk grew up in comfortable circumstances, attended outstanding institutions of higher education and lives in a serene suburb where African-Americans are thin on the ground. So calling him a highborn dilettante unversed in urban problems is not outrageous, though it is irrelevant.

After all, I would guess that on the West Side of Chicago, there are black residents who wouldn't mind seeing thousands of gang members locked up. It would not be surprising to hear sentiments similar to Kirk's coming from black conservative political figures—such as Herman Cain, a tea party favorite, or Sen. Tim Scott, R-S.C., who has a near-perfect rating from the American Conservative Union. Rush didn't question Kirk's expertise when he voted to expand background checks for gun purchases, which Rush also supports.

For Rush to now dismiss Kirk because of his background is no more legitimate than it would be for Kirk to remind everyone that Rush was a leader of the violent Black Panthers and spent time behind bars on a weapons charge. Neither approach addresses the real problems of crime in Chicago.

The congressman has every right to decry the substantive shortcomings of Kirk's proposal. But those shortcomings would exist regardless of who made it. What he has no business doing—what no one has any business doing—is using patronizing language that disparages an entire race. _

Rush wouldn't quietly endure insults like that directed at him. They are no more tolerable coming from him.