Treasury Secretary Steven Munchin, speaking on the eve of the 30th anniversary of the 1987 market crash, predicted stocks will plunge if Congress fails to overhaul taxes.

"There's no question in my mind if we don't get it done you're going to see a reversal of a significant amount of these gains," Mnuchin told Politico on Wednesday.

Mnuchin's warning -- a highly unusual one for a sitting treasury secretary -- suggests he fears a drop of at least thousands of Dow points. The average has spiked almost 5,000 points since last fall's election, a rally that President Trump often celebrates as evidence of his success.

Trump's treasury secretary told Politico that the stock market has "baked into it reasonably high expectations of us getting tax cuts and tax reform done." He predicted the market will go "up higher" if Congress succeeds on taxes.

It's true that Trump's economic agenda, including promises for "massive" tax cuts and deep deregulation, sent the stock market soaring in the weeks and months after the election.

But the market's entire post-election rally is not based solely on the anticipation of tax cuts or tax reform. Stocks have been supported by strong corporate profits, improved economic growth and extremely low interest rates.

If all markets cared about were tax cuts, then stocks should have plunged this spring and summer when Trump's political stumbles threatened his agenda. Instead, investors dialed back their bets on tax cuts by selling "high tax" stocks that should benefit from tax reform. And the broader market kept going higher.

Lately, hopes of tax reform have returned, lifting potential tax cut winners like high-tax payers and small-cap stocks.

Related: How Trump's tax plan could backfire on Wall Street

Sam Stovall, chief investment strategist at CFRA Research, said tax cut hopes have "boosted investor confidence," but they didn't alter the fundamentals that markets trade on: earnings estimates. Those projections haven't budged because details on the tax deal aren't available yet, Stovall said.

Only 32% of investors polled by E*Trade believe "President Trump and the current administration" is a leading factor behind the extended bull market in stocks. The survey respondents said that the top three drivers for stocks are: improving U.S. economy (61%), strong earnings (45%) and strong performance in certain sectors (40%).

Those positives are why Stovall isn't worried about Congress setting off a market crash.

"Should tax cuts not materialize, a pullback or mild correction may ensue, but I don't think it would trigger a new bear," Stovall said.

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Mnuchin's comments raised eyebrows because normally the U.S. treasury secretary is counted on to instill financial and economic confidence, not sow doubt.

"That is fundamentally irresponsible. He has no understanding of the role of treasury secretary," said Robert Shapiro, who served as a Commerce Department economic official under President Clinton and later advised Hillary Clinton.

"Part of the job of the treasury secretary is to maintain the stability of U.S. markets. Every other treasury secretary has recognized this. Apparently, it's eluded Mr. Mnuchin," said Shapiro, who is a senior fellow at Georgetown's McDonough School of Business.

One parallel in recent history of a treasury secretary linking the health of the market to a single piece of legislation is Hank Paulson's support for the TARP bailout in 2008. The former treasury secretary famously begged Speaker of the House Nancy Pelosi not to blow up the Wall Street rescue. The Dow plunged 777 points after the House of Representatives initially rejected the bailout.

Of course, that was a totally different time as the U.S. was grappling with the scariest financial crisis since the Great Depression. Now, big banks are healthy, unemployment is very low and markets are on the upswing -- raising the question of how much the economy really needs tax cuts right now.

Besides, just because the notoriously-fickle market expects something, doesn't mean it's the best policy for the moment.

"To pinpoint or lever policy initiatives to the direction the stock market will take seems a little short-term oriented," said Mark Luchini, chief market strategist at Janney Capital.

Ironically, Luchini said it's possible the economic expansion is extended if there is no tax deal because it would keep the Federal Reserve from fearing the economy is overheating.