Rep. Carolyn Maloney, D-N.Y., at a news conference, October 2009, on the passage of House legislation for the acquisition of land on the National Mall for the National Women's Museum. (Image Credit: Bill Clark/Roll Call/Getty Images)

President Obama took his fight for tougher gun control laws to Colorado today as the debate over gun control has gotten increasingly heated, even menacing at times.

White House spokesman Jay Carney denied suggestions that the president's gun legislation was dead, telling reporters on Air Force One on the flight to Colorado that "negotiations are ongoing on a variety of pieces of this proposal in an effort to try to find the votes necessary."

Rep. Carolyn Maloney, D-N.Y., canceled a public appearance Tuesday because of death threats she received.

"Yesterday, several death threats were phoned into my New York office in response to news reports about a bill I authored requiring gun owners to have insurance. The calls were fielded by young interns, who were understandably shaken by this experience," Maloney said in a statement emailed to ABC News today.

"Given all the acts of gun violence we have seen in the past two years, the shootings in Aurora and Newtown, the attack on my friend and colleague Gabby Gifford, I take the threat of more gun violence very seriously," Maloney said.

Brian Malte of the Brady Campaign to Prevent Gun Violence called the threats against Maloney "outrageous."

"We deplore any sort of threats like that. We need to have a national conversation and a very civil discourse about what is needed in this country," Malte told ABC News.

Other gun control advocates have received similar threats since the debate over gun laws reignited in the past year.

Colorado State Rep. Rhonda Fields received threatening emails and a voicemail attempting to pressure her to drop gun reform legislation she backs in her state. Her office released excerpts from the emails, including one from Feb. 15, full of misspellings, crude and racially-charged insults, and a reference to the shooting of Rep. Giffords.

Dudley Brown, head of Rocky Mountain Gun Owners, used an ominous double entendre when discussing his opposition to more gun laws.

"I liken it to the proverbial hunting season," Brown told NPR. "We tell gun owners, 'There's a time to hunt deer. And the next election is the time to hunt Democrats.' "

While the federal government wrestles with the gun debate, states are moving ahead on their own, often in contradictory ways. Colorado state lawmakers have already passed a law requiring background checks for all gun transfers and banning high-capacity ammunition magazines. They go into effect in July.

These laws have provoked a backlash from gun ownership advocates. At least two groups have already canceled shooting competitions in the state, citing the new laws.

New York, where Mayor Bloomberg's Mayors Against Illegal Gun Violence campaign is based, passed restrictions even more quickly than Colorado. In January, the state legislature approved the SAFE Act, making it the state with the strictest gun laws in the country.

The law includes limits on ammunition capacity, assault weapons and sales of guns and ammunition.

Connecticut lawmakers, motivated by the shooting spree that took the lives of 26 children and adults at Sandyhook Elementary School, are set to impose even stricter gun laws in a state that already had some of the strictest in the country. Other states have gone in the other direction, seeking to preserve or expand protections for gun owners.

Alaskan lawmakers introduced a bill this January that would forbid enforcing federal bans on assault rifles and high-capacity magazines, according to Alaska Public Media. Arkansas lawmakers voted to allow guns in churches. In one town in Georgia, residents who don't own a gun will be in violation of the law nine days from now.