WASHINGTON — Days after the mass shootings in Colorado, guns shifted to the forefront of the presidential campaign as President Barack Obama and Republican candidate Mitt Romney engaged in their most extensive discussions on the issue since the tragedy.

Obama, in a speech to an African-American group Wednesday in New Orleans, embraced some degree of additional restrictions on guns. He acknowledged that not enough had been done to prevent weapons from getting into the hands of criminals and pledged to work with lawmakers from both parties to move forward on the matter.

Romney said in a television interview that changing the nation's laws would not prevent gun-related tragedies. But he mistakenly said many weapons used by the shooting suspect in Aurora, Colo., were obtained illegally, despite the fact that authorities allege that the firearms used to kill 12 people and injure dozens more were purchased legally.