Washington (CNN) Vermont Sen. Bernie Sanders signaled he'll target Democratic presidential primary opponent Hillary Clinton's wealth and her Iraq War vote on the campaign trail, he said Tuesday on CNN.

"It's a problem," he said when asked by CNN's Wolf Blitzer about the fact the Clintons made more than $30 million since 2014.

"But a more serious problem is, what do we do about the grotesque level of income and wealth inequality in America today?"

The independent senator has become the de-facto presidential pick for progressives wary of Clinton's candidacy, and has made combating income inequality a central focus of his campaign. On Tuesday, Sanders introduced a bill making public colleges free for all Americans, which he'd pay for with a "very modest" tax on stock trading, which he estimated could bring in as much as $300 billion each year.

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