Today is the deadline for presidential candidates to report fundraising totals for the first quarter of the year. Several contenders for the Democratic nomination have already announced their totals, including, at the head of the pack, Sen. Bernie Sanders of Vermont, with more than $18 million in contributions. Sen. Kamala Harris, from California, raised $12 million. Sen. Elizabeth Warren of Massachusetts? $6 million. How important is that money, so early in the race?