President Donald Trump recently expressed interest in the federal government acquiring a 15% stake in a massive railroad merger — remarks that took on new resonance this week when a federal regulator put the $71.5 billion merger of Union Pacific and Norfolk Southern on pause for additional review. There’s no clear connection between the president’s comments, in a conversation with Fortune , and the delay, announced by the regulatory body, the U.S. Surface Transportation Board (STB), on May 28. A pause is not unexpected for such a huge acquisition. At the same time, Trump’s second term has been marked by unprecedented federal investments in publicly traded companies —from Intel to rare earths miners and refiners —all in industries deemed critical for national security. Trump didn’t specifically name any railroads when discussing the idea with Fortune , citing a “very big” railroad merger.…