Is Montana different? In context of campaign finance law, Supreme Court says "no"

The U.S. Supreme Court on Monday issued its decision in American Tradition Partnership, Inc. v. Bullock, the case under which the Court determined the constitutionality of Montana's campaign finance law. That law, which dates to 1912, bans corporate money from campaigns. (A law passed a few years later limits individual donations to $160/person.) The U.S. Supreme Court held on Monday that the law banning corporate money is unconstitutional because it conflicts with the 2010 decision in Citizens United.  Four justices joined in a dissent written by Steven Breyer:

Moreover, even if I were to accept Citizens United, this Court's legal conclusion should not bar the Montana Supreme Court's finding, made on the record before it, that independent expenditures by corporations did in fact lead to corruption in Montana.  Given the history and political landscape to Montana, that court concluded that the State had a  compelling interest in limiting independent expenditures by corporations.  2011 MT 328, para. 36-37, 363 Mont. 220, 235-36, 271 P.3d 1, 36-37.  Thus, Montana's experience, like considerable experience elsewhere since the Court's decision in Citizens United, casts grave doubt on the Court's supposition that independent expenditures do not corrupt or appear to do so.    

Montana Governor Brian Schweitzer published this op-ed, "Mining for Influence," about the case in the New York Times earlier this month.  In it, Schweitzer describes how Montana came to adopt the law banning corporate money.  In short, a miner William A. Clark became wealthy overnight after finding a massive copper vein.

He bought up half the state of Montana, and if he needed favors from politicians, he bought those as well.  

In 1899 he decided he wanted to become a United States senator.  The State Legislature appointed United States senators in those days, so Clark simply gave each corruptible state legislator $10,000 in cash, the equivalent of $250,000 today.  

Clark "won" the "election," but when the Senate learned about the bribes, it kicked him out.  

Schweitzer also explains the laws' consequences for Montana:

These laws have nurtured a rare, pure form of democracy.  There's very little money in Montana politics.  Legislators are basically volunteers:  they are ranchers, teachers, carpenters and all else, who put their professions on hold to serve a 90-day session, every odd year, for $80 a day. 

And since money can't be used to gain access, public contact with politicians is expected and rarely denied.

U.S. Senator Jon Tester of Montana had this to say in the the wake of Monday's Supreme Court decision:

The court's supposed to be full of smart, well-thought-out people, but they rolled back Montana 100 years, back to the time literally when millionaires and billionaires bought elections, and they did it under the guise of free speech, which is crazy.   This is really a sad day in American democracy.

It is worth noting that Tester's opponent in the upcoming election, Denny Rehberg, is well supported by groups like Crossroads GPS, whose donors are largely unidentified.

All of this left me wondering about the extent to which Montana's claim of exceptionalism relates to its rurality.  So I had a look at its brief in opposition to the petition for certiorari.  While that brief does not use the word "rural" or "nonmetropolitan," it does say this:

Issues of corporate influence, sparse population, dependence upon agriculture and extractive resource development, location as a transportation corridor, and low campaign costs make Montana especially vulnerable to continued efforts of corporate control to the detriment of democracy and the republican form of government.  Clearly Montana has unique and compelling interests to protect through preservation of this statute.  

And that, to me, those descriptors suggest rurality.  And, indeed, as of the 2000 Census, 50.2% of the state's residents lived in places with populations less than 2,500, the Census Bureau definition for a rural place.  That makes Montana one of the most rural states in the nation, at least as measured by the percentage of population who are rural dwellers.