Presidential aspirants in both parties are talking about saving the middle class. But the middle class can’t be saved unless Wall Street is tamed.

The Street’s excesses pose a continuing danger to average Americans. And its ongoing use of confidential corporate information is defrauding millions of middle-class investors.

Yet most presidential aspirants don’t want to talk about taming the Street because Wall Street is one of their largest sources of campaign money.

Do we really need reminding about what happened six years ago? The financial collapse crippled the middle class and poor — consuming the savings of millions of average Americans, and causing 23 million to lose their jobs, 9.3 million to lose their health insurance, and some 1 million to lose their homes.

A repeat performance is not unlikely. Wall Street’s biggest banks are much larger now than they were then. Five of them hold about 45 percent of America’s banking assets. In 2000, they held 25 percent.

And money is cheaper than ever. The Fed continues to hold the prime interest rate near zero.

This has fueled the Street’s eagerness to borrow money at rock-bottom rates and use it to make risky bets that will pay off big if they succeed, but will cause big problems if they go bad.

We learned last week that Goldman Sachs has been on ashopping binge, buying cheap real estate stretching from Utah to Spain, and a variety of companies.

If not technically a violation of the new Dodd-Frank banking law, Goldman’s binge surely violates its spirit.

Meanwhile, the Street’s lobbyists have gotten Congress to repeala provision of Dodd-Frank curbing excessive speculation by the big banks.

The language was drafted by Citigroup and personally pushed by Jamie Dimon, CEO of JPMorgan Chase.

Not incidentally, Dimon recently complained of being “under assault” by bank regulators.

Last year JPMorgan’s board voted to boost Dimon’s pay to $20 million, despite the bank paying out more than $20 billion to settle various legal problems going back to financial crisis.

The American middle class needs stronger bank regulations, not weaker ones.

Last summer, bank regulators told the big banks their plans for orderly bankruptcies were “unrealistic.” In other words, if the banks collapsed, they’d bring the economy down with them.

Dodd-Frank doesn’t even cover bank bets on foreign exchanges. Yet recent turbulence in the foreign exchange market has causedhuge losses at hedge funds and brokerages.

This comes on top of revelations of widespread manipulation by the big banks of the foreign-exchange market.

Wall Street is also awash in inside information unavailable to average investors.

Just weeks ago a three- judge panel of the U.S. court of appeals that oversees Wall Street reversed an insider-trading conviction, saying guilt requires proof a trader knows the tip was leaked in exchange for some “personal benefit” that’s “of some consequence.”

Meaning that if a CEO tells his Wall Street golfing buddy about a pending merger, the buddy and his friends can make a bundle — to the detriment of small, typically middle-class, investors.

That three-judge panel was composed entirely of appointees of Ronald Reagan and George W. Bush.

But both parties have been drinking at the Wall Street trough.

In the 2008 presidential campaign, the financial sector rankedfourth among all industry groups giving to then candidate Barack Obama and the Democratic National Committee. In fact, Obama reaped far more in contributions from the Street than did his Republican opponent.

Wall Street also supplies both administrations with key economic officials. The treasury secretaries under Bill Clinton and George W. Bush – Robert Rubin and Henry Paulson, respectively, had both chaired Goldman Sachs before coming to Washington.

And before becoming Obama’s treasury secretary, Timothy Geithner had been handpicked by Rubin to become president of Federal Reserve Bank of New York. (Geithner is now back on the Street as president of the private-equity firm Warburg Pincus.)

It’s nice that presidential aspirants are talking about rebuilding America’s middle class.

But to be credible, he (or she) has to take clear aim at the Street.

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That means proposing to limit the size of the biggest Wall Street banks; resurrect the Glass-Steagall Act (which used to separate investment from commercial banking); define insider trading the way most other countries do – using information any reasonable person would know is unavailable to most investors; and close the revolving door between the Street and the U.S. Treasury.

It also means not depending on the Street to finance their campaigns.