We tend to think of the government, and particularly elected officials, as being stodgy old corrupt boring people, but very little of that is actually true. (Old I'll give you pretty much right off the bat, since the average age hovers a little under 60, and Daniel Inouye of Hawaii and Frank Lautenberg of California died in office at nearly 90.) The story here begins in 1965, with a freshman senator from California named George Murphy.
George was a big fan of candy (and I can hardly criticize him for that, having a bag of gummi bears on my desk as I write this), and he started stashing some in his desk, although you're not allowed to eat on the Senate floor. Then he moved to a desk with rather higher traffic, next to one of the main doors, and started passing out his delicious treats.
Pretty soon, they started calling it the Candy Desk, and when Murphy lost reelection in 1970, other Republicans took up the baton. Paul Fannin of Arizona was the first one to do so, storing sugary snacks in his desk for the entirety of his third term. It got passed around quite a bit after that, and the desk itself was a bit mobile too, staying around that area but not being nailed down to a specific senator's working area until 1981, when Roger Jepsen of Iowa got bags of hard candy.
The heyday of the candy desk came during Rick Santorum's tenure; he held the spot from 1997-2007, when Bob Casey beat him by seventeen points. During that decade, Hershey shipped him a hundred pounds of their products four times a year, plus Just Born sending in Mike and Ikes and such. After he lost, Craig Thomas of Wyoming had the desk, but there was no single company in Wyoming big enough to hand over hundreds of dollars of candy for the Senate's enjoyment. And yes, it had to be in Wyoming, because the only reason this worked in the first place was a Senate rule allowing members to distribute products of their home state for the chamber's enjoyment. They got around this by having smaller stores give a little bit each, but Thomas died a few months later anyway.
The current occupant is Mark Kirk of Illinois, who brings gum, popcorn, jelly beans, and tootsie rolls. Democrats have another, less well-known version; the Conference Secretary, currently Patty Murray of Washington, keeps a desk in front stocked with candy that Jay Rockefeller buys with the money people give him. Rockefeller is retiring this year, and if Republican Shelley Moore Capito wins, there may be a bit of a scramble on the part of Democrats with a partisan sweet tooth.