In his most explicit critique of Hillary Clinton's email controversy to date, Democratic presidential rival Bernie Sanders told The Wall Street Journal that if the former secretary of state skirted public-records requests or compromised classified information, concerns about the issue are "valid questions."

Asked whether he regretted his remark that the American people are sick of hearing about her "damn emails" during the last debate, Sanders said in the Wednesday interview that he did not and that the investigation should "proceed unimpeded."

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“You get 12 seconds to say these things,” the senator explained. “There’s an investigation going on right now. I did not say, ‘End the investigation.’ That’s silly."

Sanders also talked about his long-standing opposition to the Trans-Pacific Partnership, in contrast to Clinton, who now opposes the deal she once called the "gold standard" of trade agreements. Consistency on issues like this "does speak to the character of a person," he said.

He also talked up his vote against authorizing the war in Iraq in 2002, remarking that “[i]t is important to see which candidates have the courage to cast tough votes, to take on very, very powerful interests."

On Wall Street, Sanders pointed to his record and support for breaking up large financial institutions and of reinstating the Glass-Steagall Act.

“I have been walking the walk, not just talking the talk,” he declared, remarking that people should be "suspect" of candidates "who receive large sums of money from Wall Street and then go out and say, ‘Trust me, I’m going to really regulate Wall Street.'"

And he still thinks his campaign is "going to pull off one of the major upsets in American history."

“We had to fight very hard in the last six months to get my name out there, to get my ideas out there,” Sanders said, noting that his campaign still has a "long way to go" with African-Americans and Latinos.