The Democratic challengers to President Trump raised tens of millions of dollars in the first months of the 2020 presidential campaign, with Senator Bernie Sanders setting the pace for the field, with $18.2 million raised.

As always, it is important to remember that winning the money race is not the goal itself but a means to an end: building a sustainable and effective campaign for the party nomination and, eventually, the White House.

But the disclosures were the first peek at what kind of campaigns the leading Democrats are constructing, with fresh investments in digital advertising, big rallies (Senator Kamala Harris’s campaign spent about $500,000 on her splashy kickoff in Oakland), and staffing nationally and in the early states. Senator Elizabeth Warren has amassed an eye-popping staff of more than 160 — spending a higher share of what she raised than any other campaign.

Whoever emerges will face a far more professionalized and better funded effort than the one that Mr. Trump led in 2016. In the first three months of the year, Mr. Trump raised more than $30 million and had more than $40 million in the bank. He and the Republican Party added another 100,000 small donors.