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Reports of a possible compromise on the Senate's gun control package will certainly be welcomed at the White House. But it cements where the debate is happening. It's not Democrat vs. Republican. It's NRA vs. the middle.

An assault weapons ban is all-but-dead, which means that the best hope for advocates of new gun restrictions is to expand background checks to cover gun sales at gun shows and for private sales. Sens. Chuck Schumer (D-NY), Joe Manchin (D-WV), Mark Kirk (R-IL), and Tom Coburn (R-OK) worked on a compromise which fell apart last month, prompting Schumer to introduce a proposal that's far stricter than most Republicans could support. Senate Majority Leader Harry Reid pushed out a vote on the issue to this month in hopes that a compromise between the parties could be reached.

Today, The Washington Post reports that it still may. Manchin is working with Pennsylvania's Pat Toomey on an agreement that could be palatable to legislators from both parties — or, at least, to at least 60 of them.

Manchin and Toomey are developing a measure to require background checks for all gun purchases except sales between close family members and some hunters, which addresses concerns of some conservatives, according to the aides, who spoke on the condition of anonymity because they were not authorized to talk publicly about the talks.

Toomey's involvement is seen as key. As the Post notes, a deal between the solidly center-focused Kirk and Manchin would be unlikely to engage anyone from either party. GovTrack.us plots each senator's political ideology on a spectrum from left to right, and his or her leadership score (based on how often the senator sponsors bills versus signing on to others') on the vertical axis.. While Toomey's no Tom Coburn, he's at least squarely in the middle of the Republican pack.

A number of the more conservative members of the Senate have joined Rand Paul in threatening a filibuster of any new rules. It's not clear that the Manchin-Toomey proposal will convince the needed five Republicans — much less the 55 Democrats and independents — that would be needed to break the filibuster. The key consideration is NRA-stoked concern that expanded background checks would lead to a national gun owner reigstry — despite such a thing being illegal under current law. (A recent poll suggests that the argument is also gaining ground with voters.) When the Post says the compromise "addresses concerns of some conservatives," it doesn't mean those who are concerned about such a registry. Toomey and Manchin have to pick up what few Republicans they can from the rest.