The Union of Concerned Scientists has placed ads in the Minneapolis-St. Paul and Denver airports, calling on Senators Obama and McCain to “get serious about reducing the nuclear threat.” Above is a picture of the ad on display in Minneapolis. (The one in Denver says “Senator Obama: It Is Time to Get Serious About Reducing the Nuclear Threat”)

Northwest Airlines has asked Clear Channel to remove the ad, calling it a strong anti-McCain message. (Click here for coverage from the St. Paul Pioneer Press and Minneapolis Star-Tribune.)

The delicious irony is that, of course, McCain has said that “the time has come to renew” our commitment “to move toward nuclear disarmament” and that “We do not need all the weapons currently in our arsenal.”

By calling the ad — which merely makes a point McCain himself has made — an “attack ad,” Northwest Airlines implicitly suggests that Senator McCain was not sincere in his comments. By contrast, no one viewed the identical advertisement in Denver, addressed to Senator Obama, as an attack.

Oh, did I mention that Northwest is the official airline of the Republican National Convenion?