On the banks of the same Rio Grande but 300 miles apart, President Joe Biden and GOP challenger Donald Trump on Thursday surveyed the U.S.-Mexico border and tussled from a distance over who is to blame for the nation's broken immigration system and how to fix it. Immigration has emerged as a central issue in the 2024 presidential campaign, which is widely expected to be a Biden-Trump rematch, and each man is seeking to use the border problems to his own political advantage. Each chose an optimal location from which to make his point, got a briefing on operations and issues, walked along the scrub brush by the Rio Grande and spoke directly to the public.