Mention bipartisan cooperation and no two names come more quickly to mind than “McCain” and “Feingold.” Ever since Republican Senator John McCain of Arizona and Democratic Senator Russ Feingold of Wisconsin began working together more than a decade ago to promote the McCain-Feingold campaign finance reform law and related clean government initiatives, they have had something of a mutual-admiration society.

In 2000, when he was running a very different campaign for the presidency, McCain told me he would seriously consider giving Feingold a job in the administration he hoped to construct.

This year, McCain still mentions Feingold — not usually in the context of discussions about his potential Cabinet. In fact, the Republican presidential nominee has even brought up his Democratic colleague in debates with Barack Obama, where McCain has sought to portray himself as a more politically flexible contender than his Democratic rival.

Feingold, for his part, has spoken well of McCain during the current presidential campaign — even as the Wisconsinite has noted their disagreements on issues of war and peace, trade policy and civil liberties.

But the increasingly crude nature of the McCain campaign’s attacks on Democratic nominee Barack Obama — and the racial and ethnic insensitivity that has been tolerated at too many rallies featuring McCain and Republican vice presidential candidate Sarah Palin — finally proved too much for Feingold this week.

On Monday, the other half of the McCain-Feingold duo called on McCain to knock it off.

Here’s what Russ Feingold said:

In a closely fought campaign like the Presidential race, elements of either side can get caught up in the emotions of the contest. This is especially true during stressful economic times. I heard Senator McCain help tamp down the rhetoric at a recent town hall meeting.

Regrettably, he needs to do more of that. An energetically waged campaign can all too easily slip over into something hateful and dangerous, and everyone from the candidate on down needs to do whatever it takes to stop that. It won’t seem credible for the John McCain I know to say his campaign should be respectful, while seeming to look the other way as his campaign employs certain tactics and rhetoric which apparently are intended to appeal to the fears of some Americans.