The end of the current economic expansion, and therefore stock market bull run, is imminent. 

While some think the end will come later rather than sooner, tariffs are becoming a larger threat to the economy, as President Trump is threatening with additional tariffs on $200 billion worth of Chinese goods. 

Union Pacific, (UNP - Get Report) , a bellwether for the U.S. economy, seems not to be adjusted investment plans based on a downturn in the U.S. economy, as its CEO Lance Fritz told TheSteet. The company is looking to spend about $3.25 per year, and isn't reducing that number for now. 

But the U.S. economy is vulnerable to external shock, as GDP growth has decelerated from 4% in the summer of 2018, to around 3% to start 2019, as one of the longest economic expansions in American history stays alive.

Fritz says there are three main threats to the economy: 

"There's clearly a connection for us between consumers buying things, the industrial economy feeling healthy, and trade," Fritz said. 

But "my big worry is, of those three, trade is the one that could be a shock that might tip over our economy, but right now things look like they're still hitting on all cylinders and I think there's still room to expand," he said. 

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Tariffs hurting the economy would hurt stocks, and particularly Union Pacific's stock. Meanwhile, the company is lokoing to return $20 billion of cash back to shareholders through buybacks, and Fritz walked TheStreet through his plan to accomplish that.