The 19th century had the Lincoln-Douglas debates. The 20th century brought Kennedy-Nixon. And now we have just experienced a forensic masterpiece to define our times: the Clinton-Sanders Debate Debate.

This particular rhetorical showdown was not a back-and-forth about issues, appropriately enough, but an argument about whether to debate — and when, and where. It began Jan. 30, when the Bernie Sanders presidential campaign challenged Hillary Clinton to debate him in Brooklyn on April 14.

Clinton suggested the Democrats instead debate in Pennsylvania, on Long Island or in Upstate New York. Sanders accused Clinton of ducking.

Clinton proposed a New York debate on the evening of April 4 — but the Sanders campaign rejected the idea as “ludicrous” because the NCAA basketball championship would be later that night and Syracuse might be playing.

Clinton proposed they debate on ABC’s “Good Morning America” on April 15, but Sanders rejected that, too.

In response to a question from an activist at a rally in Harlem, Democratic front-runner Hillary Clinton said she is "so sick of of the Sanders campaign lying." Here's some background on that incident. (Sarah Parnass/The Washington Post)

Clinton even acquiesced to the original Sanders demand and offered to debate April 14 in Brooklyn. Sorry, Sanders said. He now had a rally scheduled for that night — and the permit, his campaign said, had been hard to get.

The Sanders campaign countered Sunday by suggesting four other nights — one of them on a weekend, which it previously had said was unacceptable. Clinton summarily rejected those days.

Finally, with New York’s April 19 primary looming, Mayor Bill de Blasio on Monday intervened: If Sanders would debate on April 14, de Blasio tweeted, “I will help you secure any permit you need to ensure your NYC rally can happen too.”

Sanders late Monday acquiesced to debate on the very day and in the very place he proposed two months ago. He could rally another time at his preferred venue, New York’s Washington Square Park — which, by coincidence, was the site Saturday of the International Pillow Fight, in which hundreds of strangers playfully thumped each other with feather-filled sacks.

This is oddly appropriate, because the Democratic nominating contest generally, like the Great Debate Debate, has come to resemble a pillow fight — a lot of commotion and feathers flying, but the blows don’t have much impact. Sanders long ago ceased to have a meaningful chance of winning the nomination; he would need to win 57 percent of the remaining delegates (or 67 percent, if you include uncommitted superdelegates), which, under the Democrats’ system of assigning delegates in proportion to the vote, simply isn’t going to happen.

And Sanders, to his credit, refuses to attack Clinton on her character, which he would have needed to do to have any chance of winning. He has stepped up his attacks on Clinton’s positions, but his parries, particularly compared with those in the Republican race, are gentle. Sanders therefore can disrupt and annoy Clinton on her way to the nomination, but he can’t beat her.

Top Sanders strategists acknowledged as much in a New York Times article Monday by Patrick Healy and Yamiche Alcindor. They were quoted speaking in the past tense and lamenting what the writers described as “missed opportunities to run an aggressive political operation in 2015 that would have presented more of a challenge to Mrs. Clinton.” Sanders strategist Tad Devine said the “central complication with Bernie is that he never wanted to cross into the zone of personal attacks because it would undercut his brand.”

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The Republican National Committee is welcoming the Sanders show as a distraction from the GOP candidates’ fratricide. The RNC, in its daily media summary Monday, emailed a news article reporting that “Clinton is ‘showing flashes of frustration’ as she struggles to put Bernie Sanders away.”

But what does Sanders get from this? The Great Debate Debate shows the futility.

Early in the campaign, he and other Clinton challengers justifiably complained that the Democratic National Committee had limited the number of debates — and hidden them on weekends — to protect Clinton. But even after Clinton, responding to a surging Sanders, dropped her reluctance to debate and agreed to participate in a total of 10, Sanders continued to portray her as hiding.

Friday, he told the New York Daily News that Clinton wasn’t “willing to debate issues of importance to New Yorkers” and that Clinton’s aides were “dragging their feet.” This prompted the tabloid to do a cover saying “Don’t be a Bum, Hil!”

But when Clinton said she would debate on the day Sanders had proposed, he looked like the dog that caught the car. His campaign protested that Clinton aides were being “disingenuous” because they knew Sanders “already had locked in a park permit for a major rally” that day.

The blow landed with the weight of goose down.

Twitter: @Milbank

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