Legislation that would expand the background check system for gun sales is due to be filed Wednesday at 5 p.m. For weeks, Sens. Chuck Schumer (D-N.Y.) and Joe Manchin (D-W.Va.) have been working on the language of the bill to secure the support of Sen. Tom Coburn (R-Okla.). As of Tuesday afternoon, however, aides said they expected Coburn, who has an “A” rating from the National Rifle Association, would decline to sign as a co-sponsor, leaving Sen. Mark Kirk (R-Ill.) and his “F” rating as the main Republican face of the bill.

“We are at that point where he has to shit or get off the pot,” said a Senate Democratic aide, who predicted that Coburn would, in the end, get off the pot.

“I don’t think Coburn is going to be on the initial bill,” conceded Jim Kessler, co-founder of the centrist-Democratic organization Third Way and a former director of policy and research at Americans for Gun Safety.

The main sticking point for Coburn has been the same for weeks: if Democrats are going to demand that records of private gun sales be kept — whether by an individual gun seller, the manufacturer, or a third party — then no deal. Democrats say that keeping records of private sales is crucial to enforcing the background check system, particularly because it would help police trace back the history of a gun used in a crime. It appears this may be the provision negotiators couldn’t work out.