On a political conference call today I heard a point of view that I had not encountered before. Apparently, before BRCA in 2002, soft money donations went through party channels, meaning that the parties had control over the donation, how it was spent, rejecting donors, etc. Some have argued that the parties were more unified then, while also having a bigger tent of people participating.
By pushing the money outside control of the party, the counterintuitive result is that the parties have become more extreme. More extreme ideas on both sides are more motivational and get more dollars donated, and can be spent via PACs with little to no party influence. In some ways they can drive the party platforms because of this.
I don’t know much about it but am looking into this idea. Here are some resources if you want to do so as well.
The Brookings Institute has a paper on partisanship and campaign finance.
The Brennan Center has the opposite view.
The Heritage Foundation has an overview.