Bernie Sanders is right about the ravages wrought by a global economy on the basic economic security of millions of American families, and on their future. He is right that government is a legitimate and indeed essential tool in addressing that insecurity, in large part because no other tool is available. Left to play out, without adjustment, the economic trends driving such change are almost certain to accelerate rather than reverse.

He is right that the forces driving wealth consolidation at the top and declining household income everywhere else -- longstanding trends that are absolutely clear in the data -- cannot help but transform this country, threaten its egalitarian roots and sow the seeds of discontent and decline.

He is right about Wall Street using its wealth to buy political and legal protection to ensure that it continues to collect a disproportionate share of the nation's productivity. "There is a reason why these people are putting huge amounts of money into our political system and in my view it is undermining American democracy," as he put it in last night's Democratic debate.

And he is right that much of Wall Street has become what economists call rent-seekers, a term defined clearly and succinctly by Nobel Prize-winning Robert Shiller.

"The classic example of rent-seeking is that of a feudal lord who installs a chain across a river that flows through his land and then hires a collector to charge passing boats a fee (or rent of the section of the river for a few minutes) to lower the chain. There is nothing productive about the chain or the collector. The lord has made no improvements to the river and is helping nobody in any way, directly or indirectly, except himself. All he is doing is finding a way to make money from something that used to be free."

Martin Shkreli, who raised the price of a much-needed generic drug from $13.50 to $750, just because he could, is a rent-seeker. Wall Street firms that brush aside billion-dollar fines for breaking the law, then reward those who broke the law with huge bonuses that encourage them to do so again, are rent-seekers. CEOs who reward themselves with double-digit pay raises and arrange golden parachutes as a reward for their failure are rent-seekers. Sports franchise owners who demand taxpayer subsidies for their stadiums are rent-seekers.

Sanders is right about all of that, and more. When he says, as he did last night, that he has been making such points far longer and with more passion than Hillary Clinton, he's right. When he points out that Clinton's  financial, political and social ties to Wall Street call into question the depth of her commitment to change the system, he is right to force the question and make her explain herself.

But Clinton is right about some things too. It is one thing to correctly diagnose and draw attention to a problem, and another to be able to fix it. She is right that addressing these issues requires that you first win a national election, and having won that election it requires the ability to build congressional support for your proposals. She is right that the American people are ready -- more than ready, I think -- to hear a long-needed debate over how to make significant adjustments to a rigged system. And she is also right that those who approach the debate in terms of revolution and resentment will close more ears than they open.

Take a look at the entrance polls out of Iowa, where Sanders was able to hold Clinton to a virtual tie. He did so because he was able to run up a 19-point advantage among the 14 percent of Iowa Democrats who describe themselves as very liberal. Clinton won by 23 points among the 28 percent of Iowa Democrats who describe themselves as moderate. Look at those numbers and ask yourself which candidate, and which message, is more likely to succeed in a nation in a precarious ideological balance.

Elections matter in another way as well. Thanks to Al Gore's narrow loss in 2000, President George W. Bush was able to nominate two justices to the Supreme Court, Samuel Alito and John Roberts. If a Democrat had filled those judicial vacancies instead, the Voting Rights Act would not have been gutted in 2013. Medicaid expansion in states such as Georgia would not have been blocked. Citizens United, the 5-4 decision that destroyed campaign-finance regulation and amplified the political power of wealth, would have gone the other way. And I don't think most Americans appreciate the cumulative effect of a series of business-law decisions issued by the Roberts court that have significantly strengthened the hand of corporate America at the expense of consumers and workers.

The next president -- Republican or Democrat -- will probably name two to three new justices to the Supreme Court. Those appointees will have more influence over how we address these issues than anybody in elected office. But first, those in elected office have to put them there.

Both Clinton and Sanders agree that we stand at an historic moment, with potential historic opportunity. And whatever damage it has done to civil debate in this country, the success of Donald Trump in the Republican primaries is cracking that door open even farther. As editor of National Review, Rich Lowry recently organized that conservative magazine's collective repudiation of Trump, but he is also smart enough to realize that "what Donald Trump has identified out there in the country is too important to be left to Donald Trump."

As Lowry warns in a recent Politico column:

"The fact is that the Republican Party can't be dependent on working-class voters at the same time that its default economic agenda has little to say to them. If Trump has opened up the space for a conversation in the GOP about how to connect with these voters and their concerns, then his carnival show will have had some significant upside. If he goes down and the Republican political class carries on as if nothing had happened and conservative pundits who have twisted themselves into knots to justify Trump go back to hewing to the verities of the 1980s, nothing will have been gained except a more entertaining primary season than usual."

Pay attention to what Lowry is saying there, because it's extraordinary. He acknowledges what many Democrats have been saying for decades, that the GOP's default economic agenda does not speak to the difficulties of the voters to whom the party appeals and does not even attempt to account for the economic realities of 2016 and beyond. "Hewing to the verities of the 1980s" -- which I would assume to be Reaganesque tax cuts for the wealthy and an unfettering of corporate power -- is no longer a politically sufficient response.

So the terms of the debate are shifting. What was once set in concrete is becoming more fluid, and both parties sense it. Under the right leadership, we have, perhaps, an opportunity to do something important. And while making a statement can be exhilarating, at times like this making change is better.