For a party that counts on women, people of color and young folks for votes, it is a bit ironic that the leading candidates in the national polls are two old white guys. National poll averages from RealClearPolitics and FiveThirtyEight show Vice President Biden leading Sen. Bernie Sanders by nine points. Sen. Elizabeth Warren is in a close third place, trailing Sanders by 2-5 points.  We haven’t seen a lot of new polling out of the early states, but the model/tracker suggests that former Biden and Sanders are in the top tier in Iowa and New Hampshire, while Biden remains solidly ahead in South Carolina.

The durability of these two candidates is a testament to some important political truths. First, even in this day and age of 'viral celebrity,' it is tough to build an enduring political brand. The second is that having experience running for president is a bigger deal than many people appreciate. 

Biden and Sanders are not just the best-known candidates in the race, but they also have the most defined identities. You know what you get with them. And, that means they have a more stable base than anyone else in the field. While a late November Quinnipiac poll found that almost two-thirds of Democrats said they might change their mind on who they currently support in the primary, 43 percent of Biden voters and 49 percent of Sanders voters said that they were committed to supporting their candidate. Meanwhile, just 29 percent of Sen. Warren voters and 25 percent of former South Bend Mayor Pete Buttigieg voters felt similarly. 

And, at a time when so many Democratic voters prize electability and crave assurance, being a known quantity has a great deal of value. Biden's image as the safe, but kinda boring and gaffe-prone candidate, is well-established. And, despite worries about his age and his debate stumbles, no one has been able to overtake Biden in the 'can beat Trump' metric. The late November Quinnipiac poll found 46 percent of Democrats believe Biden "has the best chance of winning against Donald Trump in the 2020 election" — 36 points ahead of his nearest challengers. 

Sen. Elizabeth Warren was starting to cut into Biden's margin earlier this fall — with 20 percent of voters picking her as having the best chance to beat Trump in October. But, by late November, that had been cut in half to just 10 percent. Only 6 percent of voters felt Buttigieg was the strongest candidate to match up against the president. The challenge for Warren and Buttigieg is that while Biden is certainly vulnerable, the two of them are untested and unproven entities. This is why they don't get the benefit of the doubt - or the margin of error to make mistakes that Biden is given. 

If you think that the only answer to our current political moment is major structural change with no compromises and no excuses, Sanders is your guy. Despite her call for 'big, structural change,' Warren's recent triangulation on Medicare for All undercuts that message. Instead of pursuing the single-payer, Medicare-for-All plan in the first year of her presidency, she'd instead push for a robust public option that would allow Americans to keep their private insurance if they'd want it. Only in year three, when she believes that the success of this public option will be well-established, would she pursue the Sanders-style Medicare-for-All program that would prohibit private insurance. Of course, it's hard to argue that waiting three years to get your top priority implemented is 'revolutionary.' It also raises the question of what other big priorities she's willing to compromise on. 

The fact that Sanders and Biden have been through national presidential campaigns before is another reason for their durability. No matter how talented, how smart or qualified one is, running a national campaign for president is a lot harder than it looks. Only when you've been through this grueling process can you understand how to prepare for it. This gives Biden and Sanders — and their campaigns — perspective and patience. Something that even the most disciplined first-time candidates don't have. 

Now, this doesn't mean that Biden or Sanders will be the nominee. As we know, opinions about candidates change very quickly once voting begins. But, what these two candidates do have are well-known and well-defined personalities and identities. After eight months of campaigning — including many stumbles, fumbles and even a heart attack — no one has been able to surpass Biden as leader of the "restoration" and electability wing of the party, while Sanders remains the leader of the 'revolutionary' wing. 

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