GM to slash jobs and production, cancel some car models

Yeah, while Mary Barra tried to downplay the steel and aluminum tariffs in this piece, I think the link is pretty undeniable. The preceding sentence to the quote you linked here even says:

The company has said tariffs on imported steel, imposed earlier this year by the Trump administration, have cost it $1 billion.

There are a ton of other sources that are linking GM's financial troubles to the tariffs today as well.

• General Motors set to shed 14,700 jobs as slowing sales and steel tariffs bite

Michelle Krebs, an executive analyst at Autotrader, said Barra was “trying to get ahead of a potential crisis by making cuts now”. She said a confluence of factors had triggered GM’s actions: a downturn in the important China market and a potential downturn in the North American market; the dramatic shift by consumers from traditional cars to utility vehicles; and the impact of tariffs and trade issues.

• G.M. to Idle Plants and Cut Thousands of Jobs as Sales Slow

The companies have also paid a price for the tariff battle that Mr. Trump set in motion. In June G.M. slashed its profit outlook for the year because tariffs on steel were driving up its costs. The company does not import a great deal of steel into the United States, but the increased demand for domestic steel has raised prices.

Even back earlier this summer they said explicitly that the Trump tariffs were likely to force U.S. job cuts.

• G.M. Says New Wave of Trump Tariffs Could Force U.S. Job Cuts - June 29, 2018

General Motors warned Friday that if President Trump pushed ahead with another wave of tariffs, the move could backfire, leading to “less investment, fewer jobs and lower wages” for its employees.

The automaker said that the president’s threat to impose tariffs on imports of cars and car parts — along with an earlier spate of penalties — could drive vehicle prices up by thousands of dollars. The “hardest hit” cars, General Motors said in comments submitted to the Commerce Department, are likely to be the ones bought by consumers who can least afford an increase. Demand would suffer and production would slow, all of which “could lead to a smaller G.M.”