What rational business owner would onshore manufacturing back to the US when the tariffs could go away at any second?

It takes time to optimize a business to operate with only US labor- years. Why would people make this investment when they are at risk to be immediately undercut by foreign competition the moment tariffs change? This is what will decimate the market most of all--the admins unpredictable policy disincentivizes the medium term behavior they want from businesses. So people will wait and see and take the pain, money will sit on the sidelines rather than build something on an unstable foundation.