(CNN) – Two days after a gunman who police say used legally purchased firearms killed a dozen theater-goers in a Denver suburb, the nation's political leaders began debating whether stricter controls on gun access were necessary to prevent further violence.
The question of tighter restrictions on owning guns has been largely ignored in this year's presidential campaign, and Democrats, who in the 1990s were vocal in pushing for tighter gun laws, rarely address the issue today.
That silence, however, was sharply criticized by New York Mayor Michael Bloomberg, who said Sunday that President Barack Obama and Republican challenger Mitt Romney had a responsibility to lay out a strategy for combating gun violence in America.
"This requires - particularly in a presidential year - the candidates for president of the United States to stand up and once and for all say, yes, they feel terrible. Yes, it's a tragedy. Yes, we have great sympathy for the families, but it's time for this country to do something," Bloomberg said on CBS. "And that's the job of the president of the United States."
Both candidates, Bloomberg said, had records on restricting access to assault weapons. He pointed to an assault weapon ban Romney signed as governor of Massachusetts and a 2008 campaign promise from Obama to reinstate a federal ban on assault weapons.
"The governor has, apparently, changed his views, and the president has spent the last three years trying to avoid the issue, or if he's facing it, I don't know anybody that's seen him face it. And it's time for both of them to be held accountable," said Bloomberg, long an advocate for tighter access to guns.
"Leadership is leading from the front, not doing a survey, finding out what the people want and then doing it. What do they stand for, and why aren't they standing up?" Bloomberg asked.
Speaking aboard Air Force One as the president flew to meet with families of those killed in Friday's shooting, White House Press Secretary Jay Carney said Obama did not have plans to push for new laws in light of the Colorado massacre.
"The president's view is that we can take steps to keep guns out of the hands of people who should not have them under existing law. And that's his focus right now," Carney said Sunday, adding it was too early to determine how the issue would play in the election.
Despite Bloomberg's unequivocal call for tighter restrictions on guns, two leading voices Sunday questioned whether different rules would have prevented Friday's shooting.
Colorado Gov. John Hickenlooper, speaking on CNN's "State of the Union," said he was willing to consider laws that could prevent similar mass killings but expressed skepticism that any action taken by the government could thwart the actions of "delusional" killers.
"I'm happy to look at anything," Hickenlooper, a Democrat, told CNN Chief Political Correspondent Candy Crowley. "But if there were no assault weapons available, and no this or no that, this guy is going to find something. He knows how to create a bomb, and who knows where the mind would have gone."
Republican Arizona Sen. John McCain expressed a similar willingness to consider all options Sunday but said that any action taken by the government would require a certain degree of demonstrated effectiveness before being enacted.
"I think that we need to look at everything, and everything should be looked at," McCain said, also on "State of the Union." "But to think that somehow gun control, or increased gun control, is the answer, in my view, that has to be proved."
Police in Colorado say Holmes set off two gas-emitting devices before spraying the theater in Aurora, Colorado, with bullets from an AR-15 rifle, a 12-gauge shotgun and at least one of two .40-caliber handguns that police recovered.
Holmes had bought the guns legally at stores in the Denver area over the past two months, Aurora Police Chief Daniel Oates said Friday. More than 6,000 rounds of ammunition were also purchased online, according to the police chief.
Hickenlooper said the fact that Holmes purchased his weapons from different venues would have made it difficult to track his steps.
"Certainly, we can try, and I'm sure we will try to create some checks and balances on these things, but it is an act of evil," Hickenlooper said. "If it was not one weapon, it would have been another, and he was diabolical."
McCain, pointing to the gun and bomb rampage last year in Norway that left 77 people dead, questioned whether greater restrictions on guns could prevent mass shootings.
"The killer in Norway was in a country that had very strict gun-control laws, and yet he was still able to acquire the necessary means to initiate and carry out a mass slaughter," McCain said.
"We had a ban on assault weapons that expired some years ago, and it didn't change the situation at all, in my view," McCain continued, referring a measure that was in place from 1994 to 2004.
That law's leading sponsor, California Democrat Sen. Dianne Feinstein, argued the opposite Sunday, saying that since the measure expired, hundreds of people have been killed using "weapons of war."
"These weapons ought to be stopped," Feinstein said on "Fox News Sunday." "That's what my bill did for 10 years."
She continued, "I have no problem with people being licensed to own a firearm. But these are weapons that you're only going to be using to kill people in close combat. That's the purpose for that weapon."