Susan Walsh/AP Photo

President Obama said Wednesday that his plan to curb gun violence would not come to fruition "unless the American people demand it." And today, he began mobilizing his still-active presidential campaign apparatus to do just that.

Obama campaign manager Jim Messina is leading the charge, tapping the president's coveted 4 million-strong email list to share details of the White House gun plan and launch a new online petition calling for action on gun reform: "Say you stand with President Obama in tackling this critical issue," Messina wrote.

Later, tweeting for the first time since Election Day, Messina wrote: "Whoa. Early response to gun violence petition this morning very strong. Thousands of signers already."

At BarackObama.com and the campaign's other social media platforms, a push for greater progressive engagement in the gun debate is front-and-center. On the president's Facebook page, a new infographic posted this morning has been "liked" more than 114,000 times and shared 40,000 times.

This is happening as thousands of Obama campaign alumni converge on Washington, D.C., for the "Obama Legacy Conference" at the Washington Hilton on Sunday, when leaders will discuss the future of the campaign organization and the issue of guns.

Organizers are dedicating one of two scheduled " policy briefings" to gun violence, signaling the importance of the issue to the campaign as it transitions to a new phase. The other briefing is on the Federal Budget Crisis.

"The president has the most exciting campaign apparatus ever built. It's time to turn that loose," senior Obama adviser Robert Gibbs told MSNBC on Wednesday.

"It's time to turn that loose for something more than just an election. If the NRA's got a list, then Obama for America has a bigger list and it is time to get activated again," he said. "This list will get active and it will do things if the person in charge of this list asks them to do so."

That person in charge - President Obama - is expected to soon begin a campaign-style public push for his gun-control package, including events around the country to mobilize his supporters.