The last time Hillary Clinton ran for president, the longest stretch between debates from either party was 23 days — a span which came very early in the process. On average, there was a presidential primary debate every 7.5 days between April 26, 2007, and Feb. 26, 2008.

In 2012, there were 20 Republican debates, in one case landing on consecutive days.

And then there's 2016.

After the roller coaster ride of 2012 — and the exhausting debate schedule that led up to and fed into it — the Republican National Committee developed a trimmer debate cycle aimed at keeping a lid on things. It hasn't been a smashing success just yet, mind you, but the rationale is apparent.

And the Democrats, who it once seemed might not have any debates until people starting demonstrating a willingness to run against Hillary Clinton, outlined an even smaller debate cycle than their opponents. And that has now led to a lot of frustration.

While there were 15 Republican debates and 17 Democratic ones before the Iowa caucuses in 2008, this year the number of GOP debates has been more than halved (to seven) -- and the number of Democratic debates cut by more than three-fourths.

The argument, initiated by former Maryland governor Martin O'Malley but embraced by Sen. Bernie Sanders (I-Vt.), is that the party shouldn't limit itself to six debates — only four of which precede voting. Instead, voters should be given as many chances as possible to hear from the candidates, in the spirit of democratic (small "d") engagement.

That's a perfectly fair point. But there are other much more subjective reasons for Clinton's challengers to demand more debates.

The most obvious is that debates offer free publicity. Instead of paying for TV spots that hit a few thousand people at a time, debates offer candidates — especially less-well-known candidates — primetime coverage of their ideas and their handsome former-Maryland-governor faces. Carly Fiorina polled second in a recent CNN/ORC poll based almost entirely on her performances in the first two Republican debates.

Which is the next reason candidates want more debates: It can move the polls. In 2012, debates offered a chance for voters to hear from a wide range of candidates —some of whom then went on to surge in the polls. And then the surges would end, sometimes also because of what happened in the debates. It's worth noting, in the graphs above, that the biggest spikes in polling tend to come after voting starts. Obama's big surge came after Iowa; McCain was already ascendant before the voting began but took off after. In 2012, Mitt Romney and his opponents saw spikes after they did well on primary ballots. That's why we put the free TV point first.

O'Malley and Sanders also get to imply that the system is rigged. Democratic National Committee chair Debbie Wasserman Schultz — who was speaking in New Hampshire during the chanting in the video above — has been accused of curtailing the number of debates to help Clinton, whom she backed in 2008. Regardless of the veracity of that claim, it's a powerful motivator for the non-Clinton candidates. Sanders gets to bolster his anti-establishment credentials by arguing that the establishment is literally introducing roadblocks to his success. Making that point loudly doesn't hurt — especially since Clinton doesn't appear to be terribly eager for more debates.

Which overlaps with another benefit: It gives non-Clintons something to organize around. Campaigns are always looking for excuses to collect e-mail addresses and contributions. The debate schedule just so happens to provide such an opportunity.

Clinton (and the DNC) probably recognize that the outcry over the number of debates will fade as soon as the party has its first event — which is coming up in mid-October. In the meantime, as with so many other things, Clinton's best play is to keep her head down and wait. Which seems to be exactly what she plans to do.