There's a really good reason for President Donald Trump to rethink his hardline anti-immigration promise of building a costly "Great Wall" along the US-Mexico border: Many fewer people are actually trying to cross into the US illegally now than in the past. Those are the findings of a new study released as part of the Brookings Institution's Papers on Economic Activity conference and authored by University of California at San Diego economists Gordon Hanson, Chen Liu, and Craig McIntosh. "From the rhetoric during and since the 2016 presidential election, one would think that the United States continues to experience a surge of low-skilled immigration," the authors wrote.