(CNN) President Donald Trump's tariff announcement could send a direct signal to workers in the Rust Belt that his policies are looking out for them after decades of manufacturing employment decline.

Jobs in the steel and aluminum industries are concentrated in the Midwest swing stages that delivered Trump the election in 2016, according to census data. Many of these were the states that stunned the country when non-college-educated whites who had voted for President Barack Obama swung toward Trump.

Many mills are in more reliably Republican states.

The US county with the most metal manufacturing employment -- which is mostly composed of steel and aluminum manufacturing -- is Lake County, Indiana . Indiana is home to the nation's largest steel mill, Gary Works, in the city of Gary. The county with the third-most is also in Indiana, Porter County.

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