The FBI's decision to once again close its investigation into Democratic presidential candidate Hillary Clinton's usage of a private email server while serving as Secretary of State may have one railroad breathing a deep sigh of relief.

Shares of the Kansas City Southern (KSU) railroad closed up 4.01% at $91.50 Monday as investors again rallied around expectations for a Clinton win over Republican candidate Donald Trump.

A Trump presidency could rock Kansas City Southern's core business, which is shipping goods to, from and through Mexico. The railroad  derives roughly half its revenue from its Mexican operations.

Trump has repeatedly assailed the North American Free Trade Agreement (NAFTA) between the U.S., Canada and Mexico, calling it "the single worst trade deal ever approved in this country" in his first debate with Clinton on Sept. 27.

Kansas City Southern, meanwhile, calls its rail holdings and alliances part of a "NAFTA railway system."

The railroad's vice president of investor relations, William Galligan, did not reply to a request for comment on the company's stock jump.

"We think Kansas City Southern - among the U.S. and Canadian transports -- is perhaps the most apparently exposed to restrictions to NAFTA," Morningstar analyst Keith Schoonmaker said in an email.

Trump has vowed to renegotiate or withdraw the U.S. from NAFTA if elected.

"Given Trump's indications that he wants to revisit NAFTA details and his questioning the arrangement of the transpacific trade agreement, we suspect investor sentiment would be negative on Kansas City Southern shares were Trump elected," Schoonmaker said.

Schoonmaker was skeptical about the permanence of that investor sentiment if Trump wins.

"We think this would be more of a near-term phenomenon, based more on sentiment than fundamentals," he said. "Because some of Trump's verbiage is quite business friendly as well, such as agitating for lower corporate tax rates, and the impact one President can have on trade agreements is not infinite. Upon consideration of evidence in detail and hearing from many interested parties -- such as management teams from UPS, FedEx ( (FDX) ) and the railroads - one's logical opinions may evolve."

Clinton was a strong backer of NAFTA when her husband, Bill, signed it into law in 1993 while in office as President. Investors and Wall Street have generally warmed up to her as a "status quo" candidate.

If the status quo holds, Kansas City Southern, like other railroads, will still need to find solid footing in a global environment of low commodity prices. The company reported a 4% year-over-year drop from $631.9 million to $604.5 million in revenue when it posted its third quarter earnings on Oct. 18. Earnings per share fell 8.3% from $1.20 to $1.12.

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