BERLIN — Chancellor Angela Merkel’s challenger in next year’s election may have already blurted out his own “binders full of women” gaffe early in the German campaign.

Peer Steinbrück, the Social Democratic Party’s candidate for chancellor, said in an interview in the Sunday edition of the newspaper Frankfurter Allgemeine Zeitung that “Angela Merkel is popular because she gets a women’s bonus.”

The undiplomatic comment provoked immediate criticism, but it was only the latest in a series of stumbles that have plagued Mr. Steinbrück’s effort to unseat Ms. Merkel. Mr. Steinbrück has already been forced to spend the past three months defending himself over the $1.65 million he received on the lecture circuit over the past three years.

Those earnings made his calls for higher pay for the German chancellor, which appeared in the same interview, all the more perplexing. Spiegel Online, the popular Web site of the influential magazine, said Sunday that Mr. Steinbrück “stumbles from mishap to mishap.”