So what do political parties spend all that fundraised money on?

Since no one asked, here's some random fun facts I learned that don't see normally bubbling up into common knowledge:

1. TV / Radio stations are in a very weird position with respect to political advertising: One on hand, they can't refuse to air a political ad and have to offer a "slightly lower than market value" rate to political ads... but on the other hand, they themselves are liable for the content of the ad (and can refuse or can be forced to take down the ad on that basis). For example, if the ad says "Mike Jones kicked his dog" that claim generally has to be backed up with some kind of source material or the station is liable for damages. For that reason, pretty much all of these ads get submitted with heavily annotated (line-by-line) transcripts with research backing up each claim made in the ad.
2. CPP or "Cost Per Point" is the most important thing used to calculate media spend (on radio/tv and there are analogues to it for digital ads). It basically means "the cost to get an ad seen by 1% of the target audience in a given media market". This gets really interesting in some congressional races, where the district does not line up neatly with one media market. For example, you might have 20% of the district population living in an urban media market with a CPP of $415 and the rest in a sprawling exurban/rural media market with a much lower CPP of like $90 or something.
3. Snail Mail - this is still a huge part of fundraising, that doesn't get talked about as much and the way it works on the receiving/processing end is a pretty massive industry unto itself: They have these big "caging" operations where all these people open the mail and process the old-school checks (and sometimes cash) that people send in. This company called Merkle did a lot of it, so when you see that on FEC reports that's usually what that expenditure is for.
4. "Reserving" media spend. If you're familiar with the way "reserved" instances and stuff works on like AWS, this is kinda similar: If you know months ahead of time that you're going to be spending on TV ads (like lots of campaigns) you can put some money down up front and "reserve" that ad time for a lower price than you would pay later. For this reason, if you want to really make a difference with a donation to a campaign give them money early (in their first few weeks). ... which leads to the next point:
5. The timing of campaigns "getting" money is the bane of every finance director. It tends to come in at an exponential rate 2-3 weeks before election day. At that point, it's basically useless to the campaign for anything but paying off debts.
6. U.S. Senators and Members of Congress are not allowed to do anything related to their campaigns in their official government offices. They have to walk down the street to the party offices or nearby offices that their fundraising consultants have to call donors and do stuff like that.
7. There used to be a laser on the roof of the Democratic National Headquarters (it was a point-to-point networking device to a nearby building)