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    The Democratic presidential candidates will debate again tonight. Here are four things to watch

    Democratic presidential hopefuls Pete Buttigieg, Elizabeth Warren, Joe Biden, and Bernie Sanders, along with Amy klobuchar and Tom Steyer, will take the stage again Tuesday night in Des Moines, Iowa.
    Saul Loeb/AFP
    Democratic presidential hopefuls Pete Buttigieg, Elizabeth Warren, Joe Biden, and Bernie Sanders, along with Amy klobuchar and Tom Steyer, will take the stage again Tuesday night in Des Moines, Iowa.

    Tuesday night’s debate in Iowa will be the smallest, the whitest, and possibly the most important event of the 2020 campaign.

    In the six earlier debates, which had a broad array of candidates from the most diverse field in history, candidates hoped to use the platform to become better known, raise money, and qualify for the next debate.

    Tuesday’s — the last debate before the Feb. 3 Iowa Caucuses — is just about winning over voters.


    And with polls showing four candidates effectively tied in Iowa, the importance of the 9 p.m. forum increases exponentially.

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    The list of those who qualified for the CNN/Des Moines Register debate via the toughest polling and fund-raising metrics yet are: former vice president Joe Biden, Senator Bernie Sanders of Vermont, Senator Elizabeth Warren of Massachusetts, former mayor Pete Buttigieg of South Bend, Ind., Senator Amy Klobuchar of Minnesota, and billionaire Tom Steyer of California.

    Here are four things to watch:

    Take out Bernie or Bust?

    In the final stretch before voting begins, Sanders appears to be in the best position to win the nomination, if marginally. A Des Moines Register poll, which has historically predicted every Iowa Caucus winner for decades, just put Sanders on top on Friday. Sanders is also leading in New Hampshire, the next state to vote.

    Every candidate who has won both states back-to-back has won the nomination, including, Jimmy Carter, Al Gore, and John Kerry. If the folks on the debate stage want to stop Sanders, this might be their last, best shot to do so.


    Expect moderates like Biden, Buttigieg, and Klobuchar to make the pitch that Sanders is just not electable given that he is a self-described socialist who backs a Medicare for All health care system. Sanders, of course, will likely defend himself bypointing topolls suggesting he is leading Trump in pivotal swing states.

    Warren versus Sanders

    While moderates will take their swings at Sanders, the Warren-versus-Sanders dynamic deserves its own category. The pair have had an informal pact of sorts for the entire campaign, vowing not to attack each other, hoping not split up the progressives.

    But in the last few days, this pact seems to be crumbling just in time for this debate. So far, it is all aides sniping. But the candidates will surely be asked about the subterfuge Tuesday on live televison.

    Over the weekend, Politico reported Sanders aides were telling volunteers to talk up Warren’s weaknesses, including the line that she is “a candidate of the elite.” Warren told reporters that she was “disappointed” to hear that.

    Then on Monday, CNN reported that in a December 2018 meeting, Sanders told Warren he did not believe a woman could win. The network cited two sources who Warren spoke to after the meeting and two others who were familiar with the meeting. Sanders called the report “ludicrous.”


    In that meeting, there were reportedly only two people in the room. And both Warren and Sanders will be on the stage Tuesday. While Sanders is currently riding high, Warren is slipping in polls and fund-raising and needs a solid debate to get back her momentum.

    Will anyone even touch Buttigieg?

    In the last debate, Buttigieg was the one surging in the polls and was on the receiving end of a lot of arrows from his rivals as a result. (Remember, the wine cave?) This time, Buttigieg is both very much in the mix of candidates who could win Iowa, but at the same time, might not really be a major target.

    This could mean that Buttigieg could skate by while the other candidates take aim at Sanders or worry about defending themselves. But if there is one person who has bull’s-eye on Buttigieg, it might be Klobuchar, a fellow moderate Midwesterner who really needs to perform well in Iowa to stick around. The pair tends to pull from the same group of voters, polls show, and with Klobuchar trailing in fifth place, she needs to make up some ground.

    Being second best is important

    The candidates on the stage will be forced to engage in a careful balancing act: contrasting themselves with rivals — without looking mean.

    Here’s why that is particularly important: At each of the nearly 1,700 caucus locations in Iowa, a candidate has to receive 15 percent support to be considered viable. People caucusing for a candidate who doesn’t make the cut-off will have a choose another candidate to support.

    Given that the top-tier candidates are only getting about 15 to 20 percent support in statewide polls of likely Democratic caucus goers, the winner will likely be the one who is most appealing as a second choice.

    History backs up this idea. In the run-up to the 2004 Democratic caucus, former House Democratic leader Dick Gephardt succeeded in knocking former Vermont governor Howard Dean from his front-runner status. But the viciousness of his attacks also took Gephardt out of contention. And that murder-suicide situation is how John Kerry, who was in third place just weeks before the caucus, ended up winning.

    James Pindell can be reached at james.pindell@globe.com. Follow him on Twitter @jamespindell or subscribe to his Ground Game newsletter on politics:http://pages.email.bostonglobe.com/GroundGameSignUp