How people and cultures flow between San Diego and Tijuana Michael S. Malone FacebookTwitterEmail FILE - In this June 22, 2016 file photo, Border Patrol agent Eduardo Olmos walks near the secondary fence separating Tijuana, Mexico, background, and San Diego in San Diego. U.S. President Donald Trump will direct the Homeland Security Department to start building a wall at the Mexican border. (AP Photo/Gregory Bull, file)Gregory Bull / Associated Press 2016 With President-elect Joe Biden promising to address — and likely fundamentally change — the current situation at the U.S.-Mexico border, it is important that we first understand just what that situation