Translation:The senator spends a lot of money on his campaign.
"Mange" is used with things that have discrete units, things where you can count individual bits of it, like apples, or money because money is made up of individual coins/dollars. "Han har mange penge."
"Meget" is used with things and concepts that can't be counted in discrete units. "Han drikker meget vand" (compare with "han drikker mange dråber vand" = "he drinks many drops of water")