For example, after the Civil War in the U.S., politics got extremely bad due to the large numbers of voters who were veterans and were receiving money from the government. Things got less nasty after those people died.
The idea is that nowadays in the U.S., there are several ways large numbers of voters get money from the government: welfare, government employment, and government contractor employment. Speaking generally, the Democrats tend to have more voters on welfare and directly employed by the government, while the Republicans tend to have more voters in government contractor jobs. So, each party has policies that give more money to their constituents, which results in bitter political fighting.
I know I'm being hand-wavy but that's the general idea. Here are some links that support this idea:
http://www.pewresearch.org/fact-tank/2013/07/12/the-politics...
https://www.nytimes.com/2017/06/15/upshot/how-we-became-bitt...
(Also, politics after the civil war was brutal because Reconstruction was necessarily the destruction and re-building of a culture at gunpoint, that of the slave owners. Their resentment is still a poisonous factor in current US politics, Charlottesville passim)
20 years ago was 1998, the year Clinton was impeached - the politics were just as slimy 20 years ago, the reality of it was just not as readily at our fingertips as it is today.
I can't imagine that, if the Democrats win the election next month, if they vote to impeach Trump, that any of them will cry about it, ever. I can't imagine that the Republicans shed any tears over voting to impeach Clinton, either.
If something that Trump did that was good was considered revenue, and something he did that was bad was considered costs, you're saying that it has all been costs? Or do you mean that in your view his profits = revenue - costs has been negative? I'm sure you can go around the country and DC and find plenty of people who think Trump has earned revenue, so to speak, even if they think he's a net negative.
Anyway, the points are all subjective, so no-one can balance the books but each individual voter.