Despite being a late entry into the race for the Democratic presidential nomination, Michael R. Bloomberg, the billionaire media tycoon and former mayor of New York City, has surged in the polls and is winning key endorsements before he’s even on the ballot. Today, we explore the hidden infrastructure of influence and persuasion behind his campaign — and the dilemma it poses for Democrats. Guest: Alexander Burns, a national political correspondent for The New York Times. For more information on today’s episode, visit nytimes.com/thedaily.  Background reading: Who is Mr. Bloomberg? And where does he stand on the key issues?We took a look at how Mr. Bloomberg’s enormous wealth helped build a national political network, and an empire of influence, for his campaign.His run has proved complicated to cover for the media empire he owns.