In what is almost certain to be the most crowded field of Democrats running for the White House in modern history, candidates are putting a premium on efforts to stand apart from the rest of the field.

And in the first month since big-name candidates have said they will run, none have stood out more than Sen. Kamala Harris (D-Calif.), whose weeklong cross-country announcement tour generated far more online interest than any other official candidate to date.

A review of Twitter mentions by the digital media firm Echelon Insights and The Hill's analysis of Google search data both show Harris received more than twice as much online attention during the month of January as did Sen. Elizabeth Warren (D-Mass.), and far more than Sen. Kirsten Gillibrand (D-N.Y.), even though those two contenders announced their own campaigns well before Harris.

Generating online attention is crucial to modern campaigns, digital strategists said, because the list any candidate generates quickly becomes their lifeblood. Those lists build supporters, volunteers and small-dollar donors whose engagement and enthusiasm fuel the long race for the White House.

As a consequence, top Democratic digital strategists have become some of the most sought-after employees for perspective presidential candidates.

Warren nabbed Joe Rospars, who led former President Obama's digital team during the 2008 and 2012 campaigns. Harris has hired Mike Nellis, her longtime consultant who also worked for Sen. Bernie Sanders's (I-Vt.) 2016 campaign.

Those digital directors see the moment a campaign launches as their best opportunities to build email lists. An announcement is the campaign's earliest moment of maximum exposure, and the only moment that the candidate controls entirely on their own.

"The number one priority of a campaign launch on the digital side is to grow the email list. Email is still, by far, the strongest driver of small-dollar grass-roots donations, and launch is a crucial time to get names on your list so that you can call on those people in the months ahead to help grow your organization," said Laura Olin, a digital strategy consultant who is not affiliated with any presidential campaign.

A source with knowledge of Harris's rollout said the California Democrat's email list grew significantly, including by more than 20 percent in Iowa, New Hampshire, South Carolina and Nevada, the four states that will kick off the Democratic nominating process.

The Echelon Insights analysis of Twitter traffic showed Harris was mentioned nearly 2 million times over the last 30 days. In the same period, Warren was mentioned about 900,000 times, and Gillibrand received about 300,000 mentions.

Over that same period, Harris gained a quarter-million new followers on Twitter, or about 7,500 per day, according to the social media analysis website Social Blade. Warren added about 80,000 new followers. Gillibrand added 42,000 new followers.

Three other contenders who announced this month - former Housing and Urban Development Secretary Julián Castro, Rep. Tulsi Gabbard (D-Hawaii) and South Bend, Ind., Mayor Pete Buttigieg - added between 26,000 and 36,000 new followers.

"Volume of Twitter mentions is interesting in that it indicates how much attention share the political media and pundit class is giving to Harris. Twitter isn't real life, of course, but signals like that can bleed into real life," Olin said.

Of the three leading contenders, Warren maintains the most robust online presence. She has far more fans on Facebook, nearly 3.2 million, than does Harris, about 1.2 million.

Warren's campaign declined to comment on its digital strategy.

Democratic strategists have been impressed by Harris's early rollout, which began with a video on Martin Luther King Jr. Day, extended to a rally with 20,000 people in her home town of Oakland, Calif., and then to a town hall meeting in Iowa broadcast by CNN.

"There's a reason Trump lies about his crowd sizes, because crowds demonstrate support, momentum and enthusiasm," said Jon Summers, a former top aide to Senate Democratic Leader Harry Reid (Nev.) who is unaligned in the presidential contest. "When you go on a talk show, you get a little b-roll and a sound bite, but when you do something in front of a crowd the way she did you create strong visuals that can be used over and over on TV."

The three leading candidates who entered the race in January will be overshadowed, at least temporarily, as others enter the race with their own splashy moments. Sanders, Sen. Cory Booker (D-N.J.), former Vice President Joe Biden, former Rep. Beto O'Rourke (D-Texas) and former New York City Mayor Michael Bloomberg are all in various stages of planning their own campaigns.

In the world of digital fan bases, no one comes close to Sanders, whose insurgent 2016 campaign built a massive following online. Between Twitter, Facebook and Instagram, Sanders has more than 18.5 million followers - about double the reach of the next closest contender, Warren.

Sanders captured the imagination of small-dollar donors when he kicked off his presidential bid in April 2015, almost to the same degree that Harris did this year. His campaign raised $1.5 million in its first day, the same amount Harris's team said it pulled in. But Harris's campaign said it raised money from 38,000 donors - more than the 35,000 that Sanders attracted.

"These numbers reveal a campaign powered by the people," Nellis, Harris's digital director, said in a statement.