On Sunday night, in the middle of this three-day weekend and shortly after the Steelers-Broncos playoff game, the three remaining Democratic candidates for president will hold another debate.

If you ask progressive supporters of Bernie Sanders, this is because Democratic Party officials have made the cynical calculation that their chosen candidate, Hillary Clinton, will sail more smoothly to her coronation as nominee if they minimize voters' chances to compare her to her rivals. Holding relatively few debates in out-of-the-way time slots, when most people have better things to do than watch pols yapping, is one way of keeping the party's primary season off the radar.

After all, conventional wisdom holds that underdog candidates have more to gain from debating their favored opponents, and that candidates favored to win have little incentive to give underdogs a chance by debating them.

But that wisdom is being turned on its head right now in the Democratic primary. Trusted pollsters show Sanders within striking distance of Clinton in Iowa. The revered Des Moines Register poll has him within two points, hinting at yet another Clinton underperformance in the Hawkeye State. In New Hampshire, Sanders has been stronger all along and now appears to be in the lead.

That leaves Clinton facing a near future in which she fails to win either of the first two primary contests. That won't necessarily stop her from getting the nomination — one can, of course, hope — but it hints at unease or distaste for her among among rank-and-file Democrats.

The irony is that it would be in her interests rather than those of Sanders to have the debates at times when more people would tune in. She has performed better than he has in debates, which has allowed her to make up for his far greater appeal on the stump. Sanders has shown no spine or willingness to attack any of Clinton's weak points seriously in debate. Even the preternaturally limp Lincoln Chafee, when he was still in the race, challenged Clinton on primetime TV more forcefully and effectively.

Losses in Iowa and New Hampshire would not necessarily doom Clinton's candidacy. Indeed, she would still be favored to win after that because her support is more solid in states with large numbers of black primary voters. But it would be embarrassing, and it could even cause voters in those later states to give Sanders a second look.

If Sanders wants to capitalize on the party's backfiring plan to hide debates from view, his path is as clear now as it was two months ago. He must make the case to Democratic primary voters that the progressive issues they care about, global warming, income inequality, universal healthcare, campaign finance and the like, will all be eclipsed by Clinton's dishonesty and venality if she wins the nomination.

He must argue that voters who want to spend the next 11 months defending her scandals can vote to nominate her, but those who want to talk about changing society should nominate him instead. Sanders has not risen to this task so far in any of the debates. But then again, there's always Sunday night.