Electability questions persist. Anxieties about gender and sexism are resurgent. And three leading candidates are about to get yanked off the campaign trail for President Donald Trump’s impeachment trial.

Those deep uncertainties shadowed Tuesday’s Democratic debate, the last national stage for candidates running out of time to generate momentum ahead of the Feb. 3 Iowa caucuses. Months of campaigning and millions of dollars in advertising have left Democrats with a crowded top tier, and it’s unclear if the debate helped any of the candidates break out of that pack.

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Democratic presidential candidate Sen. Bernie Sanders, I-Vt.,, center, speaks as fellow candidates businessman Tom Steyer, from left, Sen. Elizabeth Warren, D-Mass., former Vice President Joe Biden, former South Bend Mayor Pete Buttigieg and Sen. Amy Klobuchar, D-Minn. listen, Tuesday, Jan. 14, 2020, during a Democratic presidential primary debate hosted by CNN and the Des Moines Register in Des Moines, Iowa. (AP PhotoPatrick Semansky)

Electability questions persist. Anxieties about gender and sexism are resurgent. And three leading candidates are about to get yanked off the campaign trail for President Donald Trump’s impeachment trial.

Democratic presidential candidate Sen. Bernie Sanders, I-Vt., listens Tuesday, Jan. 14, 2020, during a Democratic presidential primary debate hosted by CNN and the Des Moines Register in Des Moines, Iowa. (AP PhotoPatrick Semansky)

“While differences are usually amplified in the days before an election, with Trump looming over the candidates' shoulders, this primary campaign seems to be heading in the opposite direction,” said Ben LaBolt, a former White House and campaign official for Barack Obama. “Four candidates entered the debate with a fighting chance to win Iowa tonight, and four candidates left still very much in the hunt.”

Democratic presidential candidates former South Bend Mayor Pete Buttigieg, left, and Sen. Amy Klobuchar, D-Minn., right, talk during a break Tuesday, Jan. 14, 2020, in a Democratic presidential primary debate hosted by CNN and the Des Moines Register in Des Moines, Iowa. (AP PhotoPatrick Semansky)

That’s happened in fits and starts on the campaign trail, and among their surrogates on television and social media. And at times, some of those divisions did spill over onto the debate stage.

Democratic presidential candidate, former South Bend Mayor Pete Buttigieg is interviewed in the spin room, Tuesday, Jan. 14, 2020, after a Democratic presidential primary debate hosted by CNN and the Des Moines Register in Des Moines, Iowa. (AP PhotoCharlie Neibergall)

Yet none of the candidates appeared eager to play the role of intra-party aggressor, preferring instead to use their national television time to tout their own readiness for office and make the case for why they are best suited to defeat Trump.

Democratic presidential candidate Sen. Elizabeth Warren, D-Mass., left and Sen. Bernie Sanders, I-Vt., talk Tuesday, Jan. 14, 2020, after a Democratic presidential primary debate hosted by CNN and the Des Moines Register in Des Moines, Iowa. Candidate businessman Tom Steyer looks on (AP PhotoPatrick Semansky)

Democrats have also repeatedly expressed concerns that a contentious primary could weaken their eventual nominee in a general election campaign against the president — a worry born out of the heated 2016 contest between Sanders and Clinton.

The six Democrats on stage — the smallest debate field yet — strained to keep the two-hour face-off civil and substantive. They drew policy contrasts with each other on national security, health care and trade, but repeatedly shifted the focus back to their common opponent: Trump.

Democratic presidential candidate Sen. Bernie Sanders, I-Vt.,, center, speaks as fellow candidates businessman Tom Steyer, from left, Sen. Elizabeth Warren, D-Mass., former Vice President Joe Biden, former South Bend Mayor Pete Buttigieg and Sen. Amy Klobuchar, D-Minn. listen, Tuesday, Jan. 14, 2020, during a Democratic presidential primary debate hosted by CNN and the Des Moines Register in Des Moines, Iowa. (AP PhotoPatrick Semansky)

Democratic presidential candidate Sen. Bernie Sanders, I-Vt.,, center, speaks as fellow candidates businessman Tom Steyer, from left, Sen. Elizabeth Warren, D-Mass., former Vice President Joe Biden, former South Bend Mayor Pete Buttigieg and Sen. Amy Klobuchar, D-Minn. listen, Tuesday, Jan. 14, 2020, during a Democratic presidential primary debate hosted by CNN and the Des Moines Register in Des Moines, Iowa. (AP PhotoPatrick Semansky)

“While differences are usually amplified in the days before an election, with Trump looming over the candidates' shoulders, this primary campaign seems to be heading in the opposite direction,” said Ben LaBolt, a former White House and campaign official for Barack Obama. “Four candidates entered the debate with a fighting chance to win Iowa tonight, and four candidates left still very much in the hunt.”

Those four candidates — former Vice President Joe Biden, Sens. Bernie Sanders and Elizabeth Warren, and former South Bend, Indiana, Mayor Pete Buttigieg — are locked in a tight race for the top spots in Iowa and New Hampshire, which follows next on the primary calendar. Sen. Amy Klobuchar and businessman Tom Steyer also appeared in Tuesday’s contest.

The last four winners of the Iowa Democratic caucus have gone on to secure their party’s nomination. Yet that winner often emerges late, in the phase that Democrats are now entering — one where candidates typically begin drawing sharper contrasts with each other.

Democratic presidential candidate Sen. Bernie Sanders, I-Vt., listens Tuesday, Jan. 14, 2020, during a Democratic presidential primary debate hosted by CNN and the Des Moines Register in Des Moines, Iowa. (AP PhotoPatrick Semansky)

Democratic presidential candidate Sen. Bernie Sanders, I-Vt., listens Tuesday, Jan. 14, 2020, during a Democratic presidential primary debate hosted by CNN and the Des Moines Register in Des Moines, Iowa. (AP PhotoPatrick Semansky)

That’s happened in fits and starts on the campaign trail, and among their surrogates on television and social media. And at times, some of those divisions did spill over onto the debate stage.

Biden and Sanders, two candidates in their 70s who have surprised many in the party with their durability, were frequently at odds. Sanders sharply criticized Biden’s vote 17 years ago to authorize the Iraq war, saying that while he tried to stop the Bush administration, “Joe saw it differently.”

Later, in an exchange on the candidates’ standards for supporting free trade agreements, Biden questioned whether there was “any trade agreement that the senator would ever think made sense.”

Democratic presidential candidates former South Bend Mayor Pete Buttigieg, left, and Sen. Amy Klobuchar, D-Minn., right, talk during a break Tuesday, Jan. 14, 2020, in a Democratic presidential primary debate hosted by CNN and the Des Moines Register in Des Moines, Iowa. (AP PhotoPatrick Semansky)

Democratic presidential candidates former South Bend Mayor Pete Buttigieg, left, and Sen. Amy Klobuchar, D-Minn., right, talk during a break Tuesday, Jan. 14, 2020, in a Democratic presidential primary debate hosted by CNN and the Des Moines Register in Des Moines, Iowa. (AP PhotoPatrick Semansky)

Yet none of the candidates appeared eager to play the role of intra-party aggressor, preferring instead to use their national television time to tout their own readiness for office and make the case for why they are best suited to defeat Trump.

Their goal? To help voters envision them in the Oval Office next year.

“This is the moment where the candidates have to make the pivot to being presidential because the reality of caucusing or voting for a candidate is very real,” said Karen Finney, a Democratic strategist who worked for Hillary Clinton’s 2016 campaign.

Democratic presidential candidate, former South Bend Mayor Pete Buttigieg is interviewed in the spin room, Tuesday, Jan. 14, 2020, after a Democratic presidential primary debate hosted by CNN and the Des Moines Register in Des Moines, Iowa. (AP PhotoCharlie Neibergall)

Democratic presidential candidate, former South Bend Mayor Pete Buttigieg is interviewed in the spin room, Tuesday, Jan. 14, 2020, after a Democratic presidential primary debate hosted by CNN and the Des Moines Register in Des Moines, Iowa. (AP PhotoCharlie Neibergall)

Democrats have also repeatedly expressed concerns that a contentious primary could weaken their eventual nominee in a general election campaign against the president — a worry born out of the heated 2016 contest between Sanders and Clinton.

Even a jarring rift that emerged this week between Sanders and Warren, a pair of progressive allies, passed within minutes. Sanders denied he had told Warren in a private meeting that a woman can’t beat Trump; Warren stood by her assertion and made a vigorous case for nominating a female candidate.

“Look at the men on this stage,” Warren said. “Collectively they have lost 10 elections. The only people on this stage who have won every single election that they’ve been in are the women.”

Democratic presidential candidate Sen. Elizabeth Warren, D-Mass., left and Sen. Bernie Sanders, I-Vt., talk Tuesday, Jan. 14, 2020, after a Democratic presidential primary debate hosted by CNN and the Des Moines Register in Des Moines, Iowa. Candidate businessman Tom Steyer looks on (AP PhotoPatrick Semansky)

Democratic presidential candidate Sen. Elizabeth Warren, D-Mass., left and Sen. Bernie Sanders, I-Vt., talk Tuesday, Jan. 14, 2020, after a Democratic presidential primary debate hosted by CNN and the Des Moines Register in Des Moines, Iowa. Candidate businessman Tom Steyer looks on (AP PhotoPatrick Semansky)

Yet the dispute between Sanders and Warren seems likely to linger past the debate, reviving questions about whether Democrats believe a woman can defeat Trump, another anxiety stemming from Clinton’s defeat in 2016.

Sanders and Warren, longtime friends and allies, appeared to have a terse exchange at the end of the debate, with the Massachusetts senator declining to shake Sanders’ extended hand.

The debate may have been particularly important for the trio of senators on the stage: Warren, Sanders and Klobuchar. All three will serve as jurors in the Senate impeachment trial, which is expected to begin this week and will require them to spend most of the lead-up to the caucuses not on the campaign trail in Iowa, but in the Senate chamber.

“Some things are more important than politics,” Warren said. “I took an oath. If we have an impeachment trial, I will be there.”

Where voters in Iowa will turn during this next crucial phase is far less certain.

EDITOR'S NOTE — Julie Pace has covered the White House and politics for the AP since 2007. Follow her at http://twitter.com/jpaceDC