(Susan Walsh/AP)

WELCOME TO the 2014 fall congressional campaign finance bus tour. We hope you’re comfortable because what you are about to witness is breathtaking, and more than a little unsettling. Rivers of fat-cat money are pouring into our political system; the peaks of hidden finance soar ever higher. It promises to be a wild ride.

As you get settled, a reminder of important milestones: In 2010, the Supreme Court opened the door to unlimited corporate, union or individual contributions to groups that keep just enough distance from candidates to claim they are “independent.” This April, the court eliminated an overall limit on how much donors could give to candidates, parties and various other committees over the course of an election cycle. Under Chief Justice John G. Roberts Jr., the court has demolished some of the barriers to big money in national politics.

At the same time, political operatives are ramping up organizations to pump the bucks into campaign coffers. There are tax-exempt groups that are ostensibly “social welfare” organizations under Section 501(c)(4) of the Internal Revenue Code but manage to spend a lot of money on politics and are permitted to keep their donors secret. Also increasingly seen are super PACs that can raise and spend money freely and are supposed to keep their distance from candidates, except that now they are becoming increasingly focused on single candidates in campaigns, and testing the very definition of “independent.”

The admixture of court decisions and campaign finance practices will be on full display. The Post’s Matea Gold and Tom Hamburger reported this summer that the latest must-have feature in this year’s midterm elections is a super PAC funded by a rich friend or relative. Although these political action committees are supposed to be independent, The Post reported that “cozy relations between a candidate and super PAC patrons are now commonplace, both in House and Senate races.” When put behind a single candidate, these super PACs can make a difference in a tight race and all but destroy the idea of limits on campaign donations. Two years ago, we suggested these super PACs could be put out of their misery by legislation sponsored by Reps. David E. Price (D-N.C.) and Chris Van Hollen (D-Md.), and it is still a good idea. There are more of these superbeasts than ever.

Meanwhile, the well-heeled, tax-exempt 501(c)(4) groups are also casting a long shadow over the fall campaign. According to the Center for Responsive Politics, so-called dark-money spending in the midterms will easily exceed the spending records set in the last presidential election. These groups are not supposed to have politics as their primary purpose, but many of them do, or manage to skirt the rules. The Internal Revenue Service is working on new regulations governing these groups and should force them into the sunshine or put them out of business.

Welcome to the Dark Money Express. All in all, it won’t be a pretty trip.