I'd rather pay for retraining than overpaying workers in moribund industries.
Governments are pretty pathetic at choosing which industries are worth saving.
There are some circumstances in which it may be worth doing. If the issue is more the failure of the entire economy (eg cars in 2009), then there's a case for support. If there's illegal dumping (eg steel) by a country like China, then you might see if you can apply tariffs to the dumped goods from those places. And if an industry is strategically critical, then you may place orders to ensure the industry survives.
But I don't see why US steel workers should have an additional advantage in this instance. They probably already have an advantage in terms of carriage costs: they don't have to move the steel as far as foreign competitors. If they can't use that to win the order, buy the steel from somewhere like India.
Do you know that the US has agreements in place with other countries which mean that in most circumstances it is obliged to treat these sorts of things equitably? Trump's protectionist idea is probably illegal and would start a global tit-for-tat trade war. People in other countries will also start to say "only people from our country can do such and such..." meaning people in any US export business will suddenly be out of luck. Save uneconomic steel jobs and lose economically viable export jobs. Not a very good idea.
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