The 2010 Citizens United v. Federal Election Commission case is fast becoming as explosive as Plessy v. Ferguson (1896) or Roe v. Wade (1973). It took nearly 60 years before the Supreme Court reversed the Plessy endorsement of “separate but equal” treatment of the races in Brown v. Board of Education, and opponents of abortion are still waiting (probably in vain) for Roe to go.

Instead of sitting around hoping that one of the conservative justices in the 5-4 Citizens United majority will leave the high court during a Democratic administration, Americans concerned about the degradation of politics should get cracking on a constitutional amendment that does what the founders envisioned, namely return power to the people.

Exhibit A for why this is necessary is the 2012 campaign, which promises to be one of the most corrupt in U.S. history.

Notice how I didn’t say the most negative. Politics has been a contact sport since at least the election of 1804, when President Thomas Jefferson was accused (accurately, it turned out) of having an affair with “Dusky Sally” Hemings, a slave.

And expensive campaigns per se aren’t a problem. Aggregate spending on campaigns went from about $1.5 billion in 2008 to $2 billion in 2010 (an off-year election) and will almost certainly go higher this year. That would be acceptable if the donations were relatively small and transparent.

Nixon’s Bag Men

The real issue is whether we can maintain our democracy (or our republic, if you prefer) under rules that allow a tiny group of billionaires to buy presidential elections. Strangely enough, for all the members of Congress bought and sold by the rich over the last 200 years, winning the presidency, until now, has not depended on the generosity of a few wealthy men. Even when cash was delivered to politicians by shady “bag men,” the money usually went to the party or local bosses and was somewhat diffused.

When the insurance magnate W. Clement Stone gave President Richard Nixon $2 million in 1972, it looked scandalous and helped kick off post-Watergate reforms. That verges on small potatoes today, when black bags couldn’t possibly hold all the money.

The majority in Citizens United ruled that unlimited independent campaign expenditures do not “corrupt” our system. This is so wrong on the facts and so antithetical to our democratic traditions that it demands a national movement for a Fair Elections Amendment to the U.S. Constitution.

Right now, that’s still a goo-goo idea of interest mostly to wonky reformers and Occupy Wall Street protesters. There’s a widespread assumption that “process” changes don’t hit people where they live and thus won’t resonate no matter how many polls show strong public support.

Congress is so resistant to campaign finance reform that in 2010 Senate Republicans filibustered the DISCLOSE Act, which merely required a level of transparency in campaign contributions that the GOP claimed for years to favor.

So does the current climate doom any Fair Elections Amendment? Not necessarily. Let’s remember that many of the existing 27 amendments to the Constitution also began with little support. It’s the job of leaders to build momentum for change that doesn’t seem possible at the moment.

Properly harnessed, the shame of this year’s election should help build a movement for constitutional change. Americans are meeting a whole new cast of unlovable characters hellbent on being kingmakers.

Billionaire Buddies

Standing just behind Rick Santorum during his victory speech in Missouri this week was billionaire Foster Friess, who is almost singlehandedly keeping Santorum’s campaign afloat. The same for billionaire Sheldon Adelson, who savaged Mitt Romney’s character on behalf of Newt Gingrich’s campaign and without blinking has now promised to do whatever it takes to savage Barack Obama’s character on behalf of Romney. Karl Rove has already raised $50 million from a handful of wealthy individuals, many with business interests before the government. Charles and David Koch plan to raise hundreds of millions at secret meetings of the superrich that look like something out of a bad movie.

Then this week the Obama campaign signaled to backers that it welcomes unlimited multimillion-dollar contributions to the super-PAC set up by a former White House aide.

Like Obama’s decision to opt out of public financing in 2008, this may seem to make sense politically, but it undermines his bid to be a transformational president. And he gave up the moral high ground for little gain. Even if a few Wall Street executives swallow their misgivings and kick in (a big “if”), the Obama campaign will never get close to the much-publicized goal of raising $1 billion. George Soros, who helped Democrats get back the Congress in 2006, isn’t the only wealthy Democrat on the sidelines this year.

So we’re headed for a clear choice between small money and big money. At the end of 2011, the president had more than a million small donors, with most giving an average of less than $100 each; Romney’s super-PACs had fewer than 100 big donors, with most giving more than $1 million each. (His campaign’s small-donor fundraising is weak so far.)

In a little-noticed attempt to take some of the sting out of his decision, Obama tepidly endorsed (through campaign manager Jim Messina) a constitutional amendment “if necessary.” He should risk the hypocrisy rap and make it a centerpiece of his second-term agenda.

Moving reform forward requires uniting behind one of the half-dozen proposed amendments floating around. (Even hip-hop impresario Russell Simmons has one.) The only bipartisan bill -- and thus the one with the best chance over time -- is sponsored in the House by Democrat John Yarmuth and Republican Walter Jones. Their amendment, comparable to one sponsored by Tom Udall in the Senate, counters the Citizens United ruling and says money is not speech, and it authorizes Congress to enact public financing.

The specifics of how best to clean up the system are less important now than building a movement. Constitutional change is disruptive and should always be approached with caution. But the risk of the United States moving from a democracy to a plutocracy is growing stronger every day.

(Jonathan Alter is a Bloomberg View columnist and the author of “The Promise: President Obama, Year One.” The opinions expressed are his own.)

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To contact the writer of this article: Jonathan Alter at alterjonathan@gmail.com.

To contact the editor responsible for this article: James Gibney at jgibney5@bloomberg.net.