Raising such a huge sum in a short amount of time — through an email list that had never before been tapped for contributions — would make Trump’s pitch for donations one of the most successful in American politics, according to veteran fundraisers. Because not every email recipient responds to a solicitation, experts estimate that it would require a list of as many as 6 million supporters to generate $2 million in such a short period. Digital fundraising experts were skeptical that Trump has been able to curate and maintain such a big list. But if he did pull off $2 million in half a day, Democrats should be worried, they added. At such a rate, Trump could pull in $20 million online by the end of the month.