With tragic mass shootings in El Paso, Dayton, and Odessa all happening in August, Congress is returning to session with renewed calls for action on guns. Of course, this isn't the first time Congress has tried to take action after mass shootings.

In 2013, after the Sandy Hook Elementary School shooting, Congress voted down the Manchin-Toomey bipartisan proposal to expand background check requirements to certain types of private sales. Since that time there have been multiple major mass shootings, but there has not been any significant movement on Capitol Hill to advance legislation.

So what are the prospects for Congress to advance legislation on guns in the wake of August’s attacks? Is anything different this time around?

Polling in the last decade has seen a slight increase in the percent of people who support making gun laws “more strict,” with six in ten Americans now holding that position according to Gallup. When people are asked which they prioritize more, “protecting gun rights” versus “controlling gun violence,” what used to be an even split in 2013 is now a 16-point margin in favor of “controlling gun violence” according to the latest NBC/NPR/Marist polling.

At a very high level, the winds have shifted toward greater overall support for gun control.

But the details matter, and not all gun control proposals garner similar numbers of support. If polls tend to show around 60% of Americans supporting “more strict” gun laws or “controlling gun violence,” what should we make of the dramatic differences between support for various policies that purport to advance that cause?

Essentially, policies around guns break down into two groups: laws that aim to restrict who can have guns, and laws that restrict what guns people can have. In poll after poll, there is less opposition to restricting who than what, making it much more politically viable for President Trump and his allies to get behind new restrictions about red flags and background checks, yet far less likely they will touch restrictions on types of weapons or ammunition that can be purchased by law-abiding citizens.

Universal background checks have long been a popular policy, and the recent NBC/NPR/Marist polling confirms that the policy continues to earn overwhelming support, with 83% saying background checks should be required for gun shows or private sales. Also receiving strong support, with a quarter or fewer Americans opposing the policy, are increased funding for mental health screenings, national red flag laws, and requiring individuals to obtain a license before being able to purchase a gun.

But there is a drop-off in support for policies such as banning purchases of high-capacity ammunition magazines (61% support, 34% oppose) and banning the sale of semi-automatic assault-style weapons like the AR-15 (57% support, 39% oppose). They still garner majority support, but the opposition numbers rise above a third. For Republican lawmakers in red states, that kind of opposition is likely to be vocal and influential in their decision making.

It’s not hard to guess why you would see a gap in support for those two categories of reform. Law abiding gun owners who like their guns and would like the ability to procure them in the future are going to be more reluctant to get behind any reform that might hinder their own ability to purchase a firearm or ammunition. However, if they don’t have a criminal background issue or concern about getting red-flagged, policies that restrict who can buy guns may seem much less likely to affect them negatively.

Republicans considering the various gun reforms that may find less resistance from gun-owners if they are pursuing changes that are supposed to only truly affect people who ought not have guns at all, versus changes to law that will keep gun owners from being able to continue purchasing a weapon or ammunition they prefer. If you’re wondering if and how Republicans will ever budge on guns, expect it to come down to the who versus the what of gun buying.