The stakes and unpredictability of presidential debates make compelling television. The more candidates, the more unpredictable they become.
This week's Democratic debates, staged by NBC, MSNBC and Telemundo, feature more candidates than the party has ever fielded. That might leave all 20 delivering brief, introductory versions of their stump speeches, or provoke long shots to seek attention by assailing better-known rivals such as Joe Biden or Elizabeth Warren.
But recent history shows the debates can reveal the candidates' skills and character - even if the two stand at odds.
Here are five examples over the last 3 decades of what Democratic primary debates can show.
"PROFILES IN COURAGE"
In Dec. 1987, former Arizona Gov. Bruce Babbitt played Elizabeth Warren's present-day role as as the Democrat most willing to spell out a detailed presidential agenda.
When NBC anchor Tom Brokaw challenged six Democrats to stand up if they supported tax increases, Babbitt rose to his feet alone.
"Not a lot of profiles in courage here," Babbitt chided his cautious rivals.
Babbitt never took off as Massachusetts Gov. Michael Dukakis captured the Democratic nomination. GOP candidate George H.W. Bush, telling voters to "read my lips – no new taxes," won the presidency.
But events vindicated Babbitt's candor. Two years later, President Bush raised taxes.
By 1992, Democrats had lost five of the previous six presidential elections. That March, ex-Gov. Jerry Brown of California seized on fears that front-runner Bill Clinton couldn't win.
"I think he's got a big electability problem," Brown said. He cited news reports signaling conflicts of interest between Hillary Clinton's Arkansas law firm and her husband's gubernatorial administration.
Clinton flashed the focused, finger-pointing anger that would characterize his response to a later scandal. (https://www.youtube.com/watch?v=K5kUITklALQ)
"You ought to be ashamed of yourself for jumping on my wife," Clinton said. While rivals attacked him personally, he vowed to prevail as "an agent of change" on behalf of voters.
With political prowess like that, he did. But his subsequent affair with Monica Lewinsky belied his professed devotion to his wife, and in 2000 crippled the electability of his Vice President Al Gore.
"STRONG ON DEFENSE"
The 2004 Democratic debates began on May 3, 2003 – two days after President George W. Bush's "mission accomplished" speech early in the Iraq War.
Connecticut Sen. Joe Lieberman, Gore's 2000 running mate, derided rivals Howard Dean for opposing the war and John Kerry for expressing ambivalence.
"No Democrat will be elected in 2004 who is not strong on defense," Lieberman declared.
Kerry's middle-ground position prevailed; he won the nomination before losing to Bush in Nov. 2004. But Dean's stance ultimately triumphed.
In 2006, Connecticut Democrats denied Lieberman their Senate nomination and drove him from the party. In 2008, Illinois Sen. Barack Obama made opposition to the Iraq War a foundation of his presidential bid.
In an early 2007 debate, a YouTube questioner asked Democrats if they would meet without preconditions with the leaders of American adversaries Cuba, Iran, North Korea, Syria and Venezuela.
"I would," Obama immediately replied (https://www.youtube.com/watch?v=x1dSPrb5w_k). He called it "ridiculous" to refuse diplomatic conversations in the belief that it punished those countries.
Eager to cast her less-experienced rival as unprepared on national security, Clinton insisted she would not: "I don't want to be used for propaganda purposes."
The Republican National Committee subsequently mocked Obama for displaying weakness. Eventual GOP nominee John McCain did the same.
In the end Obama won, and made Clinton his Secretary of State. Before ending his term, Obama restored diplomatic relations with Cuba and struck a nuclear deal with Iran.
Today, a Republican president's approach has exceeded anything Clinton envisioned in calling Obama naïve. President Trump has held two fruitless summits with North Korea's leader; he says the two "fell in love."
"ENOUGH OF THE EMAILS"
By the first Democratic debate in October 2015, Hillary Clinton had struggled for months with controversy over her email practices as Secretary of State. But her leading rival declined to go there.
"Enough of the emails – let's talk about the real issues facing the American people," Bernie Sanders said. The in-person audience, like Clinton, roared its approval. (https://www.youtube.com/watch?v=BrBXcKcviuc)
The issue wouldn't have helped Sanders in Democratic primaries anyway. His discretion, however, did not make it go away over the following 13 months.