Most worrisome to those who advocate new gun limits is an expected amendment that would achieve one of the National Rifle Association’s biggest goals: a “national reciprocity” arrangement, in which a gun owner who receives a permit to carry a concealed weapon in any one state would then be allowed to do that anywhere in the country. Other pro-gun proposals would make it easier for dealers to sell their merchandise between states or let certain people who had been treated for mental illness regain the right to buy weapons…

Meanwhile, gun-control advocates face the possibility that the chamber might pass a bill that undercuts the current law in many respects…

If the reciprocity proposal passes in the form desired by gun rights advocates, those on both sides think it could jeopardize the entire gun-control bill.

It would make the bill unacceptable “because it so significantly overrides and undermines the states’ ability to set public safety laws,” said Arkadi Gerney, a senior fellow at the liberal Center for American Progress.