President Donald Trump will turn his signature populist rhetoric toward tax reform on Wednesday in a speech expected to tout tax cuts as a way to help workers and the middle class in an economy "rigged" against them, senior White House officials said.

With his domestic policy agenda stalled amid Republican infighting and his approval rating at just 35 percent, Trump will make his first presidential speech specifically on tax policy, an issue on he has been promising results for months.

Reiterating a 2016 campaign theme on a visit to Springfield, Missouri, Trump will say the U.S. economy is "rigged" to favor the privileged few and urge closing loopholes for the wealthy and special interests to help "Main Street."

The officials, who asked not to be identified during a conference call with reporters, said those ideas would make for a "bipartisan" message, because the notion of a rigged economy cuts across the spectrum of U.S. political ideology.

The officials said the speech would be about "why" reforming the tax code was needed, not about "how" to reform it, which is the difficult part of fixing a 70,000-page set of laws and regulations that have not been overhauled since 1986.

Trump owes his November election victory partly to his ability to get working-class Americans to support a range of business policy positions, including his call for slashing the U.S. corporate tax rate to 15 percent from 35 percent.

That connection makes Trump "uniquely positioned as a politician to make the case for an overhaul of the business side of the code and to frame it as being good for the American worker," said Rohit Kumar, a tax policy expert at accounting and consulting group PwC and a former senior Senate tax aide.

Tax reform was a major campaign promise for Trump and his Republican allies in Congress last year. But the effort has been hamstrung by repeated delays and political distractions since Trump took office in January.

The speech is unlikely to provide new details about a tax plan Trump's aides and Republican leaders in Congress are trying to hammer out in closed-door meetings in Washington.