Don't think of this as one big election, but as many, many little ones.
At the very beginning of the process, the Photography Club members approached Luna to help them design an election system, because of her interest in American politics. However, after she described the "Electrical College," or whatever the Yanks called it, they concluded that it simply wouldn't work. Four equally-sized houses would inevitably produce a tie unless some candidate could win pluralities in more than one house. Instead, the Club agreed to hold the elections on a simple first-past-the-post basis, with no runoffs or added rounds of voting. (Besides, Luna said the College and the popular vote had agreed in every election for over a hundred years. The risk of a nearly tied overall count might be greater than having the result depending on the vote of one House, but not by enough to justify the complexity.)
The ballots had been repeatedly revised as candidates had dropped out since Sunday, and now contained just four names- Susan, Hermione, Luna, and Pansy. The stacks of ballots were carefully and discreetly moved into side rooms off of the Houses' common rooms during the wee hours of Friday morning. At least one Club member would supervise each box at all times, joined by girls from each House (usually younger girls "traded" between the Houses), to prevent any form of magical or non-magical tampering.
Second-year Ravenclaw Kay Hutchison had supported Mandy Brocklehurst from the beginning. Her family lived just a couple of miles from Mandy's, and they knew each other casually. When Mandy dropped out, a disappointed Kay switched her allegiance to Luna Lovegood.
However, as Luna's campaign continued, Kay thought that Luna was getting a little... arrogant, maybe. Luna didn't bring out any new Memory Balls to explain why she was running. Kay decided to look at the other candidates' Balls to see what their arguments were.
The '3 AM' Ball from Hermione was a clincher. Kay had been born well after the War ended, but her parents had told her a little bit about it. Once or twice during the summer, she'd woken up to find her mother sitting in her room watching her sleep. Kay was no fool- you don't get into Ravenclaw if you are- and she figured that her mother was worried that something might happen to her overnight; it wasn't completely logical, but it wasn't out of the question either now that Voldemort was on the loose. She figured that Harry would need someone who knew what that felt like.
So when Kay reached the head of the line that the Ravenclaw girls had formed when the polls opened, she wasted no time in marking her ballot for Hermione Granger.
Fourth-year Hufflepuff Jo Emerson had been expecting to vote for Susan Bones from the beginning of the campaign. Hufflepuffs need to support their own, after all.
However, she also counted Hannah Abbott as a friend. Hannah was generally nice to students younger than she was, and was more willing to help them with their assignments than other sixth years. So when Jo heard about the fight between Lynn and Hannah, and she heard that Hannah had said that students should vote for Pansy instead of Susan, she was willing to believe it.
When Susan returned to Hufflepuff House after her tour on Thursday, Jo tried to ask her about the fight. Unfortunately, Susan hadn't been there and knew no more about it than Jo; when she was asked if Pansy could deserve her vote more than Susan, she simply laughed and dismissed the idea. (Like the other candidates, Susan simply hadn't taken the Slytherins' chances seriously.)
After watching Pansy’s joint Balls with Daphne and then sleeping on the matter, Jo made her decision. Pansy seemed sincere about Harry's welfare, and it just wasn't very... Hufflepuff to ridicule someone who was sincere. So after a final moment of dithering at the ballot box, before breakfast Jo voted for Pansy Parkinson.
Third-year Gryffindor Emilia Thicknesse was the niece of Pius Thicknesse, newly appointed head of the Department of Magical Law Enforcement. Influenced by Pius and other relatives, she believed that it was important for Harry to have a girlfriend who was connected with the Ministry, especially its law enforcement arm. As such, Susan Bones was the perfect candidate for her, and nothing said by any other candidate shook her beliefs at all. She happily marked her ballot for Susan before going to lunch.
Her roommate Stephanie Sanders, on the other hand, believed that Harry needed someone who wasn't quite so serious about everything. The lack of humor displayed by most of the candidates simply depressed her, and she was glad to hear a little whimsy and wit from Luna Lovegood when describing the things she enjoyed and wanted to share with Harry. So she voted for Luna early that afternoon.
And in similar fashion did some two hundred other girls make their decisions before marking their ballots. By noon, the Hufflepuffs had all voted, and their ballot box was then moved to the big open room on the eighth floor where the Photography Club members had established their operation. Shortly after classes ended, the last of the Ravenclaws did so as well.
Many Slytherins simply weren't going to vote because their interest in Harry Potter extended no further than how painfully he could be put to death. (Some with similar beliefs voted for Pansy anyway.)
Sixty-eight Gryffindors had voted as of five minutes of seven...
"Who's left again?" Tiny Barbara Michaels asked the almost equally small Dennis Creevey as they waited in the side passage outside of Gryffindor.
"Ginny Weasley and..." Creevey's response to the first-year Slytherin was cut off by the panting student who had just thrown the door open.
Fifth-year Caroline Kennedy had been so involved with her OWL studies that she had managed to forget that it was Election Day. When she remembered, she had to run from the library in a dead sprint to try to cast her vote before the polls closed. "Am I in time?" she wheezed.
"Just barely! And you are..." Dennis inquired.
"Caroline," she replied. Dennis quickly verified that she was the other nonvoting Gryffindor, and Caroline grabbed a ballot and marked it for Hermione, then slid it into the box.
A minute later, the lights went out on the bulletin boards, to be replaced with equally small red lights. The polls had closed, and the count would soon begin. The two dozen or so nonvoting Slytherins and Ginny had had their shot, as the ballot boxes locked up tight and were carried away.
The boys of the Houses were slightly puzzled to see the girls stop their conversations over the next few minutes and start moving toward the staircases leading to their rooms. Of course, most of them didn't understand girls anyway, knew that they didn't understand them, and thus didn't give the matter another thought. The few who were privy to the secret saw no need to explain anything and stayed inconspicuous so that they wouldn't have to.
Can we explain the effects of the Balls (and other influences) on some of the students? (h/t to Red Jacobson?) Yes, we can.
Can we describe the election procedure? Yes, we can.
Can we make clear how many students there are in Hogwarts (a matter on which Jo's estimates are wildly inconsistent)? Yes, we can!
Can we cruelly delay the resolution for another chapter? YES, WE CAN!
More pols' names: Kay [Bailey] Hutchison is the current senior Senator from (and probable next governor of) Texas; Jo [Ann] Emerson is a Republican Congresswoman from Missouri; Stephanie Sanders is based on Stephanie Herseth-Sandlin, Congresswoman from South Dakota; Barbara Michaels' name is based on Maryland Senator Barbara Mikulski; and Caroline Kennedy is the daughter of President John F. Kennedy and a possible next Senator from New York, replacing Hillary Clinton.