Under a recent change in Senate rules, Reid could avert a filibuster on the motion to begin debate on the gun bill by promising each party two amendments to the legislation. His aides have discussed that route, according to Politico, but the majority leader has not yet indicated whether he would use it.

Even if Reid manages to defuse a filibuster to begin debate on the bill, closing the debate is another matter entirely; Paul and his colleagues would be free to filibuster the legislation during the floor debate, ensuring that 60 votes would eventually be required to push the bill through the upper chamber.

There Reid’s task becomes significantly trickier. He could conceivably break a filibuster by peeling away enough Republicans to surmount the 60 vote threshold, but volunteers from across the aisle have been scarce: Sen. Lindsey Graham, R-S.C., has said he wouldn’t support a filibuster if senators are allowed to freely amend the legislation on the floor, but few GOP lawmakers have followed Graham’s example.