If it were that simple than no one would care if Walmart dumps a ton of goods on the market at below cost to drive its competitors out of business.

Companies always try to undercut competitors. That is just how it works when you have competitive markets. If China subsidizes steel production, the subsidy is benefitting US firms that import steel.

If there is a need for the US to have steel production capacity domestically, then why not keep steel reserves in a warehouse somewhere. This would cost a fraction of the cost of tariffs. The same rationale is used with oil reserves.

Keeping reserves costs a bit of money and requires a small number of people to administer the project. Contrast this with a tariff that props up a dead industry and results in thousands of workers being paid to work a job that shouldn't really exist and is essentially a welfare check in disguise.

Far better to use the money to directly and transparently address any resource needs, national security, etc,. and then also use money to directly and transparently provide job training to help workers deal with slower-paced but obvious economic trends.