My tax rate is 'none of your business'

Donald Trump on Friday picked a prominent climate change skeptic to help him craft his energy policy and pushed back against renewed calls that he release his income tax returns - saying his tax rate is "none of your business."

The presumptive Republican presidential nominee is seeking to build out his policy proposals as he pivots from campaigning for his party's nomination to a likely general election matchup with Democratic rival Hillary Clinton.

Among those he has asked for help is US Republican Representative Kevin Cramer of North Dakota, one of the country's most ardent oil and gas drilling advocates and climate change skeptics. North Dakota has been at the forefront of the U.S. shale oil and gas boom.

Trump's team asked Cramer, who has endorsed Trump, to write a white paper, or detailed report, on his energy policy ideas, according to Cramer and sources familiar with the matter.

Trump also took heat on Friday for not releasing his tax returns, something that American presidential candidates have done for decades. Clinton and her rival, Senator Bernie Sanders of Vermont, have both released their returns.

Trump has said the Internal Revenue Service was auditing his returns and he wanted to wait until the review was over before making them public. "It should be, and I hope it's before the election," Trump told ABC's "Good Morning America."

Pressed on what tax rate he pays, Trump refused to say. "It's none of your business," he said. The candidate has said there is nothing voters can learn from his tax filings.

Tax filings show sources of income, both from within the United States and other countries, as well as charitable giving, investments, deductions and other financial information.