TAPACHULA, Mexico — Mexican immigration authorities have broken up two small migrant caravans headed to the U.S. border, activists said Saturday. Some migrants were bused to cities in southern Mexico, and others were offered transit papers. The action comes a week after U.S. President-elect Donald Trump threatened to slap 25% tariffs on Mexican products unless the country does more to stem the flow of migrants to the U.S. border. On Wednesday, Trump wrote that Mexican President Claudia Sheinbaum had agreed to stop unauthorized migration across the border into the United States. Sheinbaum wrote on her social media accounts the same