The Dow Jones Transportation Average <.DJT>, seen as a barometer of economic health, rose after the election and closed at a record high on March 1 but is now down nearly 5 percent for the month so far.

Steel shares, which soared just after the Nov. 8 election, fell sharply this week and are down for the month of March. Also, the S&P 1500 construction and engineering index <.SPCOMCSE> is down 3.6 percent so far for March.

Along with financials, those names helped lead a post-election U.S. stock market rally, fueled by Republican Donald Trump's promises of increased infrastructure spending, tax reform and reduced regulations. The S&P 500 <.SPX> remains up 9.8 percent since the vote.

But signs that Republicans are facing difficulties uniting their majority behind a bill to replace Obamacare have caused investors to question how soon Trump's pro-growth policies may be implemented.

"Transports are the lifeblood of the economy; they are the unsung heroes of the bull market," said Peter Kenny, senior market strategist at Global Markets Advisory Group, in New York.

"They need to hold up in order to continue to provide validation to the broader trade, to the trade higher," he said, adding that he saw more room on the downside for transports and infrastructure stocks, largely because of the run up.

The transportation average on Wednesday held above the key 8,970 area, a Fibonacci retracement of its move from October to early March. A decided break below 8,970 would leave support at 8,900 and then open for a drop to the 8,760 area, another Fibonacci retracement.

"The transports are broken right now," said Andre Bakhos, managing director at Janlyn Capital LLC  in Bernardsville, New Jersey.

"We will be biding time along the way to create a consolidation or support level. Whether that starts around here or in the transports around 8,500 I don’t know."

Helping the transports on Wednesday, however, was FedEx (>> FedEx Corporation), which gained 2.1 percent after it reported mostly upbeat results late Tuesday.

The transportation average ended up 0.6 percent on Wednesday after falling 1.9 percent in the market selloff Tuesday.

Steel shares also managed to rebound from Tuesday's selloff but were still down for the month. The S&P 1500 steel index <.SPCOMSTEEL> was down 5 percent for March so far, while U.S. Steel (>> United States Steel Corporation) was down nearly 11 percent for month.

Their decline may be tied to a combination of profit-taking and other factors, though many investors likely have overestimated the infrastructure benefit to these stocks, said Charles Bradford, president of Bradford Research, a research firm.

"Some of the stocks that ran up the most get almost no benefit from construction, like U.S. Steel... Yet that was one of the big names that some people are promoting as infrastructure plays," he said.

"There's an awful lot of bad information floating out, and a lot of it comes from Washington."

(Reporting by Chuck Mikolajczak and Caroline Valetkevitch; Editing by Andrew Hay)

By Chuck Mikolajczak and Caroline Valetkevitch

Stocks treated in this article : FedEx Corporation, United States Steel Corporation