Finally it's here: a political debate without Donald Trump - although he may very well find a way to insinuate himself into the conversation. There will only be six of these Democratic forums and there are only three and a half months before Iowa voters will caucus. So the stakes are pretty high and the candidates all have to do well. Let's look at each one.

Former Secretary of State Hillary Clinton is the runaway favorite for the nomination. If there is any doubt that she is the "inevitable" nominee just ask one of her advisors and senior team. She leads in Iowa, trails in New Hampshire, as well as nationally and in every state. But she enters this debate with serious problems. First, her lead in Iowa is shrinking, which is powerful reminder of her polling position exactly eight years ago, although she went on to place third. Second, if she loses Iowa in February, she probably will not have a chance to be bailed out in New Hampshire as in 2008. If she loses both states, she could very well be perceived as too damaged by the time she reaches South Carolina with its large African American - and presumably Hillary-friendly -- constituency. Third, she is not doing well in match ups with leading potential Republican nominees and voters looking to win in November 2016 may see that she is not the right standard bearer. Fourth, a majority of voters see her as untrustworthy - a perception that could be hard to shake. Fifth, she is elusive when it comes to pinning down her core values. She has changed her positions on TPP and the XL Pipeline. And she voted for the Iraq War. Finally, she appears to lack a major theme for her run except for possibly that it is truly her turn, or that she will be the first woman President.

Mrs. Clinton needs to show that she has the requisite experience, the capacity to make tough decisions, and can bond with - in words we pollsters like to test - "with people like you and me". She has the experience but she will be challenged on whether or not she has accomplished very. Making tough decisions? This is one of the areas where her email and Benghazi responses could hurt her. And regarding bonding with the middle class, she has been a First Lady, a US Senator, and a Secretary of State for a long time. It could be hard for her.

She is a seasoned debater and her one-on-one persona can be very appealing. But a debate format does not necessarily play in her favor. A combination of tough questions from panelists and fellow candidates could hurt her. She will have to have a flawless performance to win over doubters among both Democrats and the general electorate.

Vermont Senator Bernie Sanders - he is not only the darling of the left, the leader of the progressive wing of the Democratic Party, he is doing very well in the polls. What you see is what you get with Bernie Sanders. He does not tailor his positions, he is authentic, and he is drawing huge crowds, especially with Millennials. He is a self-described Socialist, possesses the first Brooklyn-heavy accent and for a Presidential candidate rasp since Al Smith, and is known to be not so affable socially. But he offers clarity for those voters who do not prefer nuance. He has been consistent on the war in Iraq and the use of the military, on income inequality, and on the environment - all important issues for Democratic caucus and primary voters.

If Mr. Sanders were to capture the nomination, the party establishment would be apoplectic. We could see someone try to jump in after the first few primaries just to stop his march. If he wins the debate Tuesday night, we might even see a new candidate very early.

My advice to Bernie: don't change a thing. Just keep doing what you are doing because it is working. If you try to prove your electability, you may destroy your brand. As it is, you will be a key broker at the Convention.

Former Maryland Governor Martin O'Malley - it is a big surprise to me that Mr. O'Malley has not caught on. He is young, attractive, progressive, affable, successful in elections, and has a good organization in the early states. Perhaps he has been just crowded out by Mr. Sanders' attention? Whatever, the stakes are very high for him in the debate. He will be an attack dog. He will have the toughest questions for Mrs. Clinton and for Mr. Sanders. He will go after her for flip-flopping on issues, for being evasive, and for being of a generation that is retrograde. He will have to showcase his electability. He has the substance and record to pull this off. But at only about 1% in the polls, he has a lot of making up to do.

Former Virginia Senator Jim Webb and Former Rhode Island Governor/Senator Lincoln Chaffee - these are two completely different men. Mr. Webb is a rugged independent. An accomplished writer, former Cabinet member, and gadfly Senator. Mr. Chaffee has been a Republican and independent. He is more low key and eclectic on issues. Both men will vie for the position of being the most interesting, conscience-driven candidates. They deserve attention.