Democratic presidential candidate Bernie Sanders wants several guarantees for America's middle class, including free tuition at public universities and health care available to everyone. Those programs, according to an estimate by the Wall Street Journal, could cost the nation up to $18 trillion.

But in an interview on "CBS This Morning," Sanders defended his campaign goals and fired back at the Wall Street Journal, saying that paying for his plans will hinge on holding the wealthiest Americans accountable.

"We are going to ask the wealthiest people in this country who are doing phenomenally well, and many large corporations that are making billions of dollars of profits and not paying a nickel in taxes, to in fact start paying their fair share of taxes," Sanders said early Friday.

When pressed if that meant he would tax the highest income bracket at 90 percent to pay for his proposals, Sanders responded that he didn't believe that was necessary.

"I don't think you have to go up to 90 percent," the Vermont senator said. "We will come up with some very specific ideas." For those ideas, he suggested looking to "every other major country on earth" and asking how they pay for universal healthcare and tuition.

Sanders, who now leads Democratic polls in two key states ahead of Hillary Clinton, did propose a specific goal: He would like to raise the corporate tax rate.

"If you want tuition-free public colleges and universities -- which I believe we will have -- we will have a tax on Wall Street speculation which will more than pay for that," he said. Sanders also promised to "end the fact that profitable corporations in some cases in America today pay zero in federal taxes because they stash their money in the Cayman Islands and Bermuda."

And when it comes to the $18 trillion price tag put forth by the Wall Street Journal analysis, Sanders countered that the newspaper didn't take into account private health care plans.

"What the Wall Street Journal said was that included 15 billion dollars for national health care programs," the Democratic hopeful said. "What they forgot to say is that you would not be paying -- and businesses would not be paying -- for private health insurance."

He fired back at the newspaper with harsher words on a later appearance on CBSN, saying their prediction was "wrong. It was inaccurate. That's what the Wall Street Journal does."

Sanders also addressed the recent controversy surrounding Donald Trump's comments questioning President Obama's religion and birthplace.

"I think it's a disgrace to again question whether or not the president of the United States was born in this country or whether he's a Christian," Sanders said. "I thought we were beyond that. It's an outrage."

He added that American politics should not focus on "this mythology and this ugliness that suggests that the president of the United States was not born in America."

"We all remember Trump was one of the leaders of this effort a year ago," Sanders continued. "I thought maybe he had learned something from that."

Sanders added on CBSN that Trump's comments were "pathetic" and that "it's time we got beyond that, it's time we ended racism in this country."