LAS VEGAS — Democratic vice-presidential nominee Tim Kaine on Monday opened a new line of attack on Donald Trump, saying the Republican’s tax plan would benefit “debt-fueled” real estate investors such as himself.

Kaine seized on what he called a “king of debt” tax shelter during a pair of appearances here in Nevada, a battleground state, keying off news reports last week about a little-noticed aspect of Trump’s emerging tax plan.

The senator from Virginia accused Trump of “a kind of tax trickery” that, in some cases, would mean taxpayers were subsiding Trump’s real estate investments, which are often financed through borrowing.

“This would bust the deficit wide open, but it sure would help the Republican nominee, Donald J. Trump,” Kaine said at a rally at a labor union training center. “There’s just no way we should do this. It’s absolutely madness.”

During a speech last week in Detroit, Trump suggested letting businesses make immediate write-offs for investments in equipment and buildings, rather than requiring them to spread those deductions over multiple years, as a means to stimulate the economy.

In recent days, Trump advisers have been quoted in The Washington Post and the Wall Street Journal saying he also wants to continue the practice of allowing interest deductions on business loans, something House Republicans have proposed phasing out.

The two policies together can result in “negative tax rates” for businesses making investments financed with debt, economists say.

Trump advisers maintain the Republican nominee is still working through details of his tax plan — but Kaine said Trump’s intent is clear.

“It’s a kind of tax trickery that means he will pay a negative tax rate on his investments, which means the American taxpayer will pay him for making debt-fueled investments,” Kaine told a crowd at the Local 525 Plumbers and Pipefitters Training Center.

Earlier Monday, Kaine made a similar argument during an address to a national conference of ironworkers at the Mirage hotel and casino.

In front of a labor audience, Kaine chided Trump for blocking the efforts of workers at a hotel he owns here to unionize.

“We can’t let somebody with so little respect for workers sit behind the desk in the Oval Office," Kaine said.