Recent mass shootings, particularly the one at an elementary school in Newtown, Conn., in December, which claimed the lives of 20 first-graders, have ignited a much-needed national discussion about how to curb gun violence.Debates are playing out before city councils, school boards, state legislatures and Congress. Proposals range from banning sales of certain types of firearms and ammunition, to regulating gun shows at government-owned facilities, to allowing teachers to carry guns to defend their students.In Fort Worth, which has 12 gun shows scheduled this year at the city's Will Rogers Memorial Center, officials have been asked to revisit an issue the City Council tabled after vigorous debate 13 years ago. The Tarrant County Democratic Party's executive committee backs three policy changes for these shows: Allow only licensed sellers, mandate background checks for all gun sales and require a seven-day wait for those sales.While these might seem like worthy steps, there's reason to doubt whether they're within the city's power. Travis County, which was considering banning gun shows at county-owned facilities, backed off last month after Texas Attorney General Greg Abbott suggested that "they better be ready for a double-barreled lawsuit."Abbott later told the Austin American-Statesman that he wasn't planning a suit but that others would probably challenge such a ban based on a 1990s Houston case involving that city's attempt to add gun show regulations. In 2000, the 5th U.S. Circuit Court of Appeals upheld a District Court ruling that said cities don't have the authority to supersede a state law regulating "the transfer, private ownership or keeping of firearms."More restrictions -- or outright bans -- on firearms sales at city-owned facilities would likely push gun shows to private facilities, where there might be even fewer controls and safety provisions. Dallas has not had a gun show in its Convention Center since 2002, as they tend to be held at the privately owned Market Hall.The shows at Will Rogers generate revenue for Fort Worth -- more than $200,000 projected this year -- and the city has oversight of the premises. If the city were to attempt to add restrictions like background checks, enforcement would be difficult if not impossible as hundreds of individual sales take place in a single day. And officials must ask whether different local rules would help achieve the ultimate goal of curbing gun violence.Efforts to regulate gun show sales, such as closing the so-called loophole that allows private sales without background checks, would more properly be directed to the Legislature or Congress.