Coming into the week, Obama's agenda appeared to be at an important juncture — with guns, immigration, and deficit-reduction talks at various stages of progress. Winning an expansion of the background check, even as bolder gun measures failed, would have given Obama momentum to push the other two items.
Conversely, his rivals may now feel emboldened to block Obama's entire agenda. In their most cynical moments, Republican leaders privately cheer themselves with the fact that a president's approval rating usually suffers amid gridlock.
Obama's team took news of the defeat hard Wednesday, with some advisers predicting that gun regulation won't be revived. It is hard for them to explain the failure of a measure supported by 90 percent of the public without making the president appear weak.
"I can't understand it. I really can't," said Sen. Joe Manchin, D-W.Va., who tried to save the bill by joining with Republican Sen. Pat Toomey of Pennsylvania on an amendment.
David Axelrod, the president's top consultant, chastised a handful of Senate Democrats from conservative-leaning states who opposed Obama.
"Show some courage," Axelrod said on MSNBC. "Is it worth holding those jobs simply to sit there and be called a United States senator?"
In addition to Senate Republicans, of course, there were others to blame:
The GOP-controlled House. House Republicans, most of whom come from heavily conservative districts, were expected to reject any measure sent by the Senate. That made it almost impossible for Obama to keep Senate Democrats in line: Is it fair to demand that a senator risk his or her seat on a bill destined to die in the House?
The gun lobby. The National Rifle Association and other groups funded by the gun industry distorted the debate with false assertions and bullying. Among the worst offenders was the National Association for Gun Rights, which wrongly accused Republican congressmen of working with Obama to create a federal registry and confiscate guns.
Sen. Rand Paul. The likely GOP presidential candidate helped the NAGR raise money and knew of its lies, but refused to denounce them.
Obama deserves credit for trying. He lobbied lawmakers directly, traveled frequently, engaged families of the Sandy Hook victims, flexed the untested muscle of the OFA, and spoke eloquently about the need for gun regulation.
It's hard to overcome challenges that are inherent. While polls show broad support for background checks, they also show a deep distrust of Obama among conservative voters, particularly in red states. Democratic Sen. Mark Pryor's supporters will tell you the only thing more dangerous than backing gun control in Arkansas is backing Obama — on anything.
Also, the passions of gun-rights supporters are measurably greater than the intensity of gun-control advocates.