The Democratic race for the White House has been filled with twists and turns, including Sen. Kamala Harris Kamala HarrisPelosi: Trump Supreme Court pick 'threatens' Affordable Care Act What Kamala Harris' VP nomination means to us Harris slams Trump's Supreme Court pick as an attempt to 'destroy the Affordable Care Act' MORE (D-Calif.) and former Rep. Beto O’Rourke (D-Texas) dropping out before the Iowa caucuses and the late entry of former New York City Mayor Michael Bloomberg Michael BloombergBloomberg rolls out M ad buy to boost Biden in Florida Democratic groups using Bloomberg money to launch M in Spanish language ads in Florida Bloomberg pays fines for 32,000 felons in Florida so they can vote MORE.

Yet for all the surprises, there have also been two consistencies: the steady strength in national polls of former Vice President Joe Biden Joe BidenBiden says voters should choose who nominates Supreme Court justice Trump, Biden will not shake hands at first debate due to COVID-19 Joe Biden should enact critical government reforms if he wins MORE and Sen. Bernie Sanders Bernie SandersTrump, Biden will not shake hands at first debate due to COVID-19 Sanders tells Maher 'there will be a number of plans' to remove Trump if he loses Sirota reacts to report of harassment, doxing by Harris supporters MORE (I-Vt.).

The two veteran politicians started out 2019 with advantages over their rivals.

ADVERTISEMENT

They had the highest name ID among voters at the start of the year given Biden’s eight years as former President Obama’s vice president and the run Sanders made for the Democratic presidential nomination in 2016 — a race that made him a household name.

As the new year approaches, Biden and Sanders are the two favorites to win the Democratic presidential nomination.

The polling averages kept by RealClearPolitics tell the tale of durability by Biden, 77, and Sanders, 78.

On Dec. 27, 2018, Biden had an average of 27.3 percent support. Sanders stood in second place with 18 percent.

On Dec. 27, 2019, Biden leads with an average of 27.9 percent support. Sanders has 19 percent.

While Biden and Sanders have drawn consistent support, the rival candidates seeking to catch them have had different trajectories.

O’Rourke, fresh off a better-than-expected showing in his Texas Senate race against Republican Ted Cruz Rafael (Ted) Edward CruzSenate GOP set to vote on Trump's Supreme Court pick before election Supreme Court fight pushes Senate toward brink Crenshaw looms large as Democrats look to flip Texas House seat MORE, was in third place in the RealClearPolitics average one year ago, with 8 percent.

ADVERTISEMENT

Harris stood in fourth place with 4.8 percent, narrowly ahead of Sen. Elizabeth Warren Elizabeth WarrenOvernight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds On The Money: Half of states deplete funds for Trump's 0 unemployment expansion | EU appealing ruling in Apple tax case | House Democrats include more aid for airlines in coronavirus package Warren, Khanna request IG investigation into Pentagon's use of coronavirus funds MORE (D-Mass.) at 4.5 percent. Just behind them was Sen. Cory Booker Cory Anthony BookerSunday shows preview: Lawmakers prepare for SCOTUS confirmation hearings before election The movement to reform animal agriculture has reached a tipping point Watchdog confirms State Dept. canceled award for journalist who criticized Trump MORE (D-N.J.) with 4 percent.

One year later, O’Rourke and Harris are out of the race, while Booker failed to make the stage for last week’s Democratic debate. His average in the RealClearPolitics account og national polls is now 2.5 percent.

Warren has had the most movement in the polling. On Oct. 8, she jumped ahead of Biden to take the lead in the national polling average with 26.6 percent, a statistical tie with Biden’s 26.4 percent.

That represented a watershed moment for Warren in the average; on Friday she was at 15.3 percent.

South Bend, Ind., Mayor Pete Buttigieg Pete ButtigiegBillionaire who donated to Trump in 2016 donates to Biden The Hill's Morning Report - Sponsored by Facebook - GOP closes ranks to fill SCOTUS vacancy by November Buttigieg stands in as Pence for Harris's debate practice MORE is now in fourth place in national polling with 8.3 percent, followed by Bloomberg with 4.9 percent, Sen. Amy Klobuchar Amy Klobuchar3 reasons why Biden is misreading the politics of court packing Social media platforms put muscle into National Voter Registration Day Battle lines drawn on precedent in Supreme Court fight MORE (D-Minn.) with 3.5 percent and tech entrepreneur Andrew Yang Andrew YangBiden's latest small business outreach is just ... awful Doctor who allegedly assaulted Evelyn Yang arrested on federal charges The Hill's Campaign Report: Biden weighs in on police shootings | Who's moderating the debates | Trump trails in post-convention polls MORE with 3.4 percent.

Of course, national polling is just one barometer in the presidential race.

Most of the candidates are focused on Iowa and New Hampshire, which will host the race’s first two contests in February.

Here, the tale of 2019 is a bit different.

On March 10, 2019, the first day RealClearPolitics showed an average for Iowa, Biden led with 28 percent. He was followed by Sanders with 20 percent, Harris with 12.5 percent, Warren with 10 percent and O’Rourke with 5.5 percent. Buttigieg at the time was polling at 1 percent.

Flash forward to Friday and it is a very different story.

Buttigieg is now in the lead with a 22 percent average in Iowa, followed by Sanders with 20 percent, Biden with 18.8 percent and Warren with 16 percent. All four candidates, along with Klobuchar, are fighting to the finish ahead of the caucuses.

On Feb. 28, Biden had a 25 percent average in RealClearPolitics's collated polling in New Hampshire, followed by Sanders at 24.3 percent, Harris at 12 percent and Warren at 8.3 percent.

On Friday, Sanders led in the aggregate polling with 19 percent, followed by Buttigieg at 17.7 percent, Biden at 14.3 percent and Warren at 13.3 percent.

The numbers in Iowa and New Hampshire, where Biden looks to be an underdog, shows how the Democratic race remains a dogfight despite the more stable national polling.

ADVERTISEMENT

The field has already narrowed substantially, but more candidates are likely to drop out if they lose both of the first two contests.

The race has been colored by an obsession among Democratic voters to find a candidate who can defeat President Trump Donald John TrumpBiden says voters should choose who nominates Supreme Court justice Trump, Biden will not shake hands at first debate due to COVID-19 Pelosi: Trump Supreme Court pick 'threatens' Affordable Care Act MORE. While that is always a goal of a presidential primary for the party out of power, it is particularly striking among Democrats wanting to limit Trump’s presidency to four years. And it appears to have helped Biden, who has had some inconsistent moments on the Democratic debate stage.

After Iowa and New Hampshire, the Democratic primary turns to more diverse states: Nevada and South Carolina.

This is where Biden looks stronger, at least for now.

While there have been comparatively fewer polls in Nevada, Biden has led in every single one and has a 9-point lead in the aggregate over Warren, with 29 percent to her 20 percent. Sanders is statistically even with Warren at a 19.8 percent average.

Buttigieg is farther behind, with a 7.3 percent average. In the most recent polls in November and December, Biden garnered between 24 percent and 33 percent, compared to 18 to 22 percent and 18 to 23 percent for Sanders. Buttigieg’s high-water mark in a Nevada poll is 9 percent.

South Carolina, where Biden has had a huge lead for much of the year, tells a similar story.

ADVERTISEMENT

Biden has a 35 percent average in the RealClearPolitics average for South Carolina, compared to 16.3 percent for Warren, 15.3 percent for Sanders and 7.7 percent for Buttigieg.

In the most recent poll of South Carolina from the Post and Courier, however, Biden’s lead is narrower. He won 27 percent support, compared to 20 percent for Sanders and 19 percent for Warren.

There are likely to be more twists and turns in the Democratic race ahead.

It’s unclear whether Iowa will elevate its victor, dramatically changing the nature of the races in South Carolina and Nevada. But if history is any indicator, it is likely to do so.

Biden and Sanders look like they could survive losses in both of those states given their strengths in Nevada, South Carolina and other states. That’s a little less clear for Buttigieg and Warren, who would seem to need to win — or at least perform very strongly — in Iowa and New Hampshire.

Bloomberg’s candidacy is historic, and he is strafing television networks and social media sites with advertising. That could make him a contender when more than a dozen states hold contests on this year’s Super Tuesday on March 3.

The durability of Biden and Sanders, who suffered a heart attack in early October while on the trail, is also likely to color the contest ahead. Their numbers suggest some loyalty among their supporters.

It’s a fool’s errand to try to predict the Democratic primary’s outcome. A year ago, few would have believed that O’Rourke, 47, and Harris, 55, would already be out of the race at this point.

But it is clear that for someone else to win, they will have to go through Biden and Sanders. And the battle could come down to those candidates.