Supply bottlenecks tend to push up prices, but the impact varies by sector. Mr Clemens, Ethan Lewis of Dartmouth College and Hannah Postel of Duke University have found that excluding 500,000 temporary Mexican labourers from farms in the 1960s led mostly to more mechanisation. However, robots remain no match for humans when it comes to picking strawberries.Today the consequence would either be higher costs, or another unpalatable outcome for the Trump administration, such as a wider trade deficit.