The Hill reports on a new move by Senate Democrats that is interesting for a number of reasons:

Senate Majority Leader Harry Reid on Tuesday introduced a bill that would require background checks to be run on anyone buying explosive powder, a reaction to last week’s Boston Marathon bombing. […]

Under current law, people can buy up to 50 pounds of explosive “black powder” with no background check, and can buy unlimited amounts of other explosive powders, such as “black powder substitute” and “smokeless powder.”

The bill, which was first spearheaded by Senator Frank Lautenberg, would require a background check for purchase of any of those powders. The Hill adds that it would permit the attorney general to block such sales if the check reveals the would-be buyer as a suspected (or known) terrorist, or if there is grounds for believing the explosives will be used in service of terrorism:

“It defies common sense that anyone, even a terrorist, can walk into a store in America and buy explosive powders without a background check or any questions asked,” Lautenberg said Tuesday. “Requiring a background check for an explosives permit is a small price to pay to ensure the safety of our communities.”

Beyond the practical goal of this measure — making it harder for would-be bombers to build bombs — it will inevitably be seen in the context of the debate over background checks on private gun sales. That’s because some gun owners use black powder substitute and smokeless powder to produce homemade bullets, one expert tells me.

“These would be used by people that do what we call reloading,” David Chipman, a retired 25-year ATF agent who is a senior adviser to Mayors Against Illegal Guns, says. “They take spent casings and reload them with these powders. It’s done by people who want to save money on ammunition, and people who just like reloading. It’s sort of a hobby for some people and an economic issue for others.”

The “gun rights” crowd has opposed certain efforts to make it easier to track such explosive powders in the past. The National Rifle Association and gun manufacturers successfully opposed an effort to place “identifying taggants” in them designed to make it easier to trace powder used in bombs back to a buyer at a point of sale.

So how will “gun rights” Senators react to the new proposal for background checks on powders? I’ve reached out to four leading Senators — Ted Cruz, Marco Rubio, Mike Lee, and Mitch McConnell, all of whom filibustered to block any debate on the Toomey-Manchin compromise. Three of their offices — those of Cruz, Rubio, and McConnell — say they’re evaluating the proposal.

Aside from the substantive merits of the proposal, one of the political goals here is to challenge Republicans by testing just how far they are willing to go in opposing governmental action of this kind. “We’re trying to see if there’s any way to get them to Yes on background checks,” a Democratic aide tells me. The idea — as it has been with the effort to reach compromise on fiscal matters and other issues — is to keep putting ever more reasonable proposals on the table to see if there is anything that Republicans are willing or ideologically able to support or if there is any common ground to be found anywhere.