In Colorado, a state of hunters and sportsmen, the Democrats who control state government acted last month not only to expand background checks for gun sales but also to ban the kind of high-capacity magazines that gunmen have used in recent mass shootings in Newtown, Conn., Aurora, Colo., and Tucson, Ariz.
But in Washington, a federal ban on high-capacity magazines faces long odds, as the Democratic White House has been struggling to get traction on its broad gun agenda even in the Democratic-led Senate.
The reason for the disparity lies not just in the complicated, emotional politics of guns in the United States -- there was fierce lobbying in opposition to Colorado's new gun laws, and threats were even reported against some lawmakers who supported it -- but also in the way that the Senate's arcane rules make it so much harder to pass bills there than in the nation's statehouses.
Even as gun control advocates grew optimistic Tuesday that they would be able to muster the 60 votes needed to overcome a threatened filibuster, it was evident that the Senate bill was unlikely to include many of the steps that President Barack Obama initially called for after Adam Lanza killed 20 first-graders and six adults in Newtown in December with a semi-automatic rifle and several 30-round magazines.
A federal assault weapons ban -- which the president called for again this week at an emotional rally in Connecticut -- will not be included in the Senate's main gun bill. A ban on high-capacity magazines appeared in doubt as well. Most of the frenzied last-ditch negotiations in Washington were aimed at salvaging a measure that had seemed almost assured of passage in the Senate just months ago: universal background checks for gun sales, which have overwhelming public support and which a number of Republican senators had appeared open to earlier in the year.
Why has it been so much harder for Senate Democrats to pass gun bills than it was for Colorado Democrats? The answer lies in the unforgiving math of Senate procedure. Colorado's most contentious new law, which banned magazines that hold more than 15 rounds of ammunition, passed its state Senate with 51 percent of the vote and no Republican support. But because of the rules of the U.S. Senate, Democrats effectively need 60 percent of the vote to overcome the threat of filibusters and pass legislation there.
That contrast helps explain why the nation's post-Newtown gun debate has not always followed the script that some predicted in the immediate aftermath of the shooting. New gun restrictions in Colorado, New York, Connecticut and Maryland went further than many advocates on both sides had initially expected. At the national level, though, the president has faced an even steeper climb than many expected as he has labored to persuade the Senate to act on expanded background checks.
Not that passing new gun regulations in the states was easy.
An increasingly urban Colorado relishes its frontier image, and its Democratic governor, John W. Hickenlooper, had seemed cool to gun control in the past. But a combination of timing and tragedy paved the way for the bills that passed there last month. Many Democrats were galvanized to act after a gunman strode into a movie theater in Aurora in July and opened fire on the full midnight house, killing 12, wounding dozens and evoking painful memories of an earlier shooting: the 1999 massacre at Columbine High School.
Then Democrats won control of both houses of the state Legislature in November, putting action within reach. In mid-December, Hickenlooper said the time had come to re-examine the state's gun laws. Then came the Newtown shooting. Lawmakers knew they did not have much time.
"We meet 120 days out of the year," said Rep. Dominick Moreno, a Democrat from Commerce City, northeast of Denver. "You can't fiddle around like Congress does."
The opposition was fierce. Gun owners thronged the Capitol, and opponents of gun restrictions circled the building in their cars one day, honking loudly enough to be heard inside. An airplane circled overhead another day towing a banner that read, "Why does Hick hate guns?"
Groups on both sides hired lobbyists, including some firms with ties to Hickenlooper and Democrats in the legislature. The National Rifle Association, the National Shooting Sports Foundation, firearms manufacturers and a group called Rocky Mountain Gun Owners opposed the measures. Mayors Against Illegal Guns, the group founded by Mayor Michael R. Bloomberg of New York, joined with the Colorado Association of Chiefs of Police and local gun control groups to support the bills.
Pressure mounted when Magpul, a Colorado company that makes magazines, placed an ad in The Denver Post threatening to leave the state, taking much-needed jobs with it.
"A magazine ban will do more than hurt public safety in a free Colorado," the ad said. "It will force a Colorado company to leave the state."
One lawmaker pushing to ban high-capacity magazines, Rep. Rhonda Fields, a Democrat from Aurora whose son, Javad, was fatally shot in 2005, said she received a threatening letter in February.
"I'm coming for you," it said, using a racial epithet.
Not every measure passed. A bill that would have banned concealed weapons on college campuses failed, after a rape victim testified against it and was questioned aggressively -- and, many said, insensitively -- by Democratic lawmakers, setting off a backlash. And Democrats made some concessions to gun owners: Mike McLachlan, a Democratic representative from rural southwestern Colorado who wears a bolo on his website, helped raise the magazine limits in the bill to 15 rounds from 10. It was not enough for some of his constituents, though. He is now facing an effort to recall him from office.
Colorado also passed a bill requiring background checks for private gun sales -- the kind of measure that gun control advocates have made their priority in Washington. But while universal background checks once seemed likely to pass the Senate, their fate is far from clear now.
In the immediate aftermath of the Newtown shooting, more than a half-dozen Republican senators went on record with at least qualified support for expanded background checks. Sen. Dean Heller, R-Nev., called it "a reasonable step forward."
But those voices have largely gone to ground, with the lawmakers unwilling to sign on to any of the background check proposals circulating.
Some Democratic aides worry that Obama might have let the emotions of Newtown slip away. The Senate was in a rare and extended session in January, but instead of moving immediately, the president asked Vice President Joe Biden to convene a task force on gun violence. The proposals made were along the lines of what many Senate Democrats had expected in the days after the Newtown shooting, but time was lost.
Since then the search for Republican support to get the needed 60 votes has not been smooth.
Looming over the bill are concerns about whether any measure can pass the Republican-led House. Rep. Ed Perlmutter, D-Colo., said the steep climb any gun bill faces in the House makes it hard to persuade Senate Democrats from Republican-leaning states to support gun bills.
"Those senators, if they're going to vote for something, they want to know it can pass," he said, "and everything is going to have a hard time in the House."
By MICHAEL COOPER, JACK HEALY and JONATHAN WEISMAN
The New York Times