Treasury Secretary Steven Mnuchin sent U.S. stock prices to a daytime high Thursday when he said the Trump administration will produce an ambitious plan to overhaul the U.S. tax code “soon.”

But it’s not the first time the administration has promised an imminent plan, and the obstacles to a sweeping tax-code rewrite of the sort Mnuchin described Thursday haven’t gotten any smaller. A key Senate committee has yet to see final details of a White House plan, a congressional aide said. And tax-related challenges presented by the 2010 Affordable Care Act remain in place amid Republicans’ disagreement on how to dismantle the health-care law they’ve criticized for years.

On top of that, House Speaker Paul Ryan’s proposal to tax U.S. companies’ domestic sales and imports -- while exempting their exports -- has stirred controversy among U.S. businesses, created conflict among Republicans and has yet to win President Donald Trump’s endorsement.

So even as stock traders welcomed Mnuchin’s pledge to enact comprehensive tax legislation before the end of this year, skeptics questioned the prospect.

“Clearly they’re saying what they’d like to believe is true,” said Jared Bernstein, a senior fellow at the Center on Budget and Policy Priorities, a progressive policy group in Washington. “We now know that we must heavily discount their assertions,” said Bernstein, who served as former Vice President Joe Biden’s chief economic adviser.

David Fuller's view

Mnuchin’s success in bringing forward a commercially attractive tax plan, or otherwise, will probably be the biggest single factor in determining the extent of Wall Street’s stock market reaction / correction before significantly higher levels are seen.