Sen. Pat Toomey and his Democratic colleague Joe Manchin of West Virginia Wednesday unveiled a legislative proposal to subject more gun purchases to background checks.

“Candidly, I don’t consider criminal background checks to be gun control. I think it’s just common sense,” Toomey said.

Both acknowledged that today’s announcement was the beginning of a longer process.

“I’ve not taken a very high profile role on this issue,” Toomey said. “What became apparent to me in the course of this debate, there is the danger that we might end up accomplishing nothing, and not making progress where we could.”

“Today is just the start of a healthy debate that must end with the Senate and House hopefully passing these common sense measures, and the President signing it into law,” Manchin said.

The details of the proposal are forthcoming, but the broad strokes are these: the bill would require anyone purchasing guns at a gun show or online to pass a background check. it would not affect private sales.

The bill contains some incentives for gun rights advocates, including loosening rules for transporting guns across state lines and for members of the military to purchase firearms more freely.

Both Manchin and Toomey said the bill could serve as a foundation for eventually enacting universal reciprocity for concealed carry permits nationwide.

At present, some estimate that upwards of 40% gun sales occur without a background check. That includes John Shick, the man who went on a 2012 shooting spree at the Western Psychiatric Institute and Clinic in Pittsburgh.

The bill would impact firearm sales at gun shows and online, but it’s not clear whether the Manchin-Toomey bill would have prevented someone like Shick from obtaining his firearms. Manchin said the proposal specifically does not include a requirement for checks on individual gun sales.

The two must navigate a difficult political issue, and one over which Senators are already divided.

Several conservative Republican Senators have promised a filibuster against any gun-related legislation. Some red-state Democrats may join them. Liberal Democratic Senators are pushing for more stringent gun rules, but a handful of blue-state Republicans have said they would vote for cloture on a limited, background checks-only bill.

The National Rifle Association pooh-poohed the idea of background checks in general, but did not mention the Toomey-Manchin proposal specifically.

“Expanding background checks at gun shows will not prevent the next shooting, will not solve violent crime and will not keep our kids safe in schools. While the overwhelming rejection of President Obama and Mayor Bloomberg’s ‘universal’ background check agenda is a positive development, we have a broken mental health system that is not going to be fixed with more background checks at gun shows,” the release said. “The sad truth is that no background check would have prevented the tragedies in Newtown, Aurora or Tucson.”

Toomey repeatedly sought to soothe potential conservative opponents to to proposal.

“The worries that we hear sometimes about background checks leading to an erosion of our second amendment rights – that simply hasn’t happened. And we’ve got to make sure that it doesn’t.”

The Senate will debate the measure over the next week or two and Democratic leadership has given assurances that they will allow Republicans to offer numerous amendments. The Manchin-Toomey bill would be the first amendment offered.

And that’s before it reaches the GOP-controlled House, where opposition is likely to be even tougher.

Toomey said he’s spoken to several members of Congress from Pa. and they – especially those in eastern Pa. – seemed supportive of the proposal.

The bill is a major priority for President Barack Obama, who vowed action in the wake of the Newtown, Connecticut school shooting. But to sustain the possibility of passing any gun legislation, Obama and other Democrats have had to scale back the scope of their efforts. Gone, for example, are calls for a politically difficult assault weapons ban.