There are a number of potential problems with the idea that erecting trade barriers will protect American jobs. Let us look at a few of the most important problems.
First, American trade barriers will probably lead to the creation of foreign trade barriers. If we take protectionist measures, other countries will likely retaliate. This could seriously reduce the number of American jobs in sectors of the economy that rely on exports. It could also slow the world economy in general, which is not a good thing for the United States.
Second, protectionist policies might hurt American consumers more than they help American workers. If we erect trade barriers, we will effectively be raising prices on almost everything we buy. Things that we used to get as inexpensive exports will either disappear or become more expensive. This will harm all Americans.
Third, the overall quality of American jobs could go down if we enact protectionism. Right now, American workers are freed from having to do the sorts of low-skilled jobs that typically go into things like making clothes. If we stop trading, those jobs would come back to America, but they would also take up a large chunk of our work force. This would cut down on the number of workers available to do high-level jobs. Our economy would not grow as much because we would have jobs, but they would not be good jobs.
These are the major problems with the idea that more trade barriers will create more jobs.