Imagine for a moment that the purpose of a presidential debate is to elucidate policy differences on matters of concern to American voters – instead of engaging the leading Democrats in still more boring babble about Hillary Clinton’s email habits or Bernie Sanders’ socialist sympathies.

What might a diligent debate moderator ask, if she is seeking substance and happens to have done her homework?

One urgent issue that has received too little attention – and sharply divides the Democratic candidates — is the fate of the Export-Import Bank, an independent federal agency that provides financing for the export of goods and services produced by American companies. Thanks to hard-right Republicans in Congress, who have denounced the bank as a sinkhole of “crony capitalism,” its financial authority lapsed last July, endangering thousands of American jobs that are being transferred to countries where such government financing is available.

Sanders has repeatedly denounced the bank as an example of “corporate welfare” and says killing it will “protect American taxpayers and workers.”

It is true that ExIm Bank financing is made available to companies like General Electric, which shouldn’t require federal largesse, but it is also true that the great majority of its loans are made to small business exporters. The Bank costs taxpayers nothing because it runs at a profit, returning more than $7 billion to the Treasury since 1995. Its default rate is far below one percent and its backers point out that more than 50 other countries use similar agencies to bolster job creation here.

ExIm Bank supporters include most industrial unions and the AFL-CIO, whose president Richard Trumka demanded last month that the Senate act to save the bank immediately. “Any [further] delay,” said Trumka, “would jeopardize the economic future of thousands of American families.”

So why would labor ally Sanders – unlike every progressive Congressional Democrat — join with reactionary Republicans to oppose reauthorization, which Clinton supports?

Yet another macro-economic matter that deserves deeper discussion is Massachusetts Senator Elizabeth Warren’s proposal to reinstate the Glass-Steagall Act, a Depression-era statute that prohibited banks with federally insured deposits from engaging in stock trading.

Its repeal was signed in 1999 by President Clinton as part of a broader financial deregulation — which some economists, such as former Clinton Labor Secretary Robert Reich, have blamed for the high-risk and sometimes crooked speculation that led to the crash in 2008. Other economists, including former Clinton Treasury Secretary Lawrence Summers, have insisted that Glass-Steagall repeal didn’t cause the crash.

This is a dispute worth exploring, especially because Clinton is so often accused of excessive affection toward Wall Street. Sanders has announced his support for Warren’s bill, which has no chance of Congressional approval in the near future, while Clinton has said she would not support reinstating Glass-Steagall. Someone should ask her to explain clearly: Why not? Both she and Sanders should be asked to explain whether they believe that financial deregulation caused the Great Recession – and what steps should be taken to prevent another speculative disaster.

The Democratic candidates ought to be asked about their differences in dealing with the most challenging issue of our time: global climate change. It is easy enough to denounce the denialists on the Republican side, whose abject obedience to the Koch brothers and the dirty-energy industry is perfectly obvious. Both Sanders and Clinton have suggested ambitious clean energy objectives. Clinton and her husband have long advocated the expansion of solar, wind, conservation, and other alternative sources of power. 

But so far the former secretary of state has failed to endorse a tax on carbon emissions, which the senator from Vermont supports and many experts believe is essential if the world is to avoid a climate calamity. She should explain her objections. It is literally the burning issue of our time.

Photo: Democratic presidential candidate and former Secretary of State Hillary Clinton shakes hands with rival candidate and U.S. Senator Bernie Sanders (L) and thanks him for saying that he and the American people are sick of hearing about her State Department email controversy and want to hear about issues that effect their lives as they participate in the first official Democratic candidates debate of the 2016 presidential campaign in Las Vegas, Nevada October 13, 2015. REUTERS/Lucy Nicholson