Ten of the Democratic presidential candidates during the first 2020 debate. | Drew Angerer/Getty Images The candidates agree on universal background checks and an assault weapons ban. There’s less agreement on other proposals. In response to recent mass shootings in El Paso, Texas ; Dayton, Ohio ; and now Odessa and Midland, Texas , and Mobile, Alabama , supporters of stricter gun laws have voiced a simple mantra : “Do something!” So, after little federal action on guns for more than two decades, what would the 2020 presidential candidates actually do? President Donald Trump, for his part, doesn’t seem interested in much. He has supported a federal red flag law, which would allow police to take away someone’s guns if there’s some proof of a risk of violence (a “red flag”). But on other measures, from universal background checks to an assault weapons ban, Trump and Republican lawmakers have resisted, instead talking up questionable connections between violence, mental illness , and...