Colorado Democrats advanced aggressive gun-control proposals after a 12-hour marathon debate Friday in a state wrestling with its history of heartbreaking shootings and Western heritage where gun ownership is treasured by many.

Democrats moved forward with new ammunition magazine limits and universal background checks. But they withdrew two of the most controversial pieces of the package, including a gun ban on college campuses and a measure to hold assault-weapon owners liable for damages caused by their weapons.

The Colorado debate is being watched nationally as a bellwether of how far politically moderate states are willing to go with new gun laws in the wake of mass shootings in a suburban Denver movie theater and a Connecticut elementary school. It's also playing out in a state where one of the nation's most high-profile school massacres -- the 1999 Columbine High School shootings -- took place.

Already the White House has weighed in, with Vice President Joe Biden phoning four lawmakers while on a recent ski vacation here to nudge the Democrats during their first major gun debate last month.

Democratic Senate President John Morse claimed victory in the state's overall gun-control debate, even as he conceded the battle grew ugly.

"Cleansing a sickness from our souls doesn't come easy. It's gruesome," Morse said in a short speech announcing the withdrawal of his assault-weapon liability measure.

Morse's comments punctuated a nasty, drawn-out debate that drew thousands to the state Capitol over recent days. The gun package jammed legislative emails, prompted several gun-supporting businesses to threaten to leave Colorado and left one man facing criminal charges for threatening messages he allegedly sent a Democratic sponsor of some of the bills.

Friday's gun debate stretched past 12 hours, with Republicans in the Senate taking turns trying to defeat the gun controls. Democrats pulled the two most divisive bills before Republicans could speak against them. At least three Democrats were planning to side with the GOP, a margin big enough to defeat those measures.

A formal Senate vote on the measures is required next week before the bills clear the Senate. Republicans took to Twitter immediately after debate concluded late Friday to urge changed votes by Monday.

Throughout the marathon debates Friday, Republicans argued the gun controls wouldn't reduce gun violence and that mental health treatment should be expanded instead.

"We can make as many laws as we want. Until we change the hearts of man, they're going to continue to do evil things," said Sen. Scott Renfroe, R-Greeley.

Democrats have argued the country's mass shootings painfully illustrate the need for tighter gun controls. They insist the measures don't compromise Colorado's gun-loving heritage.

"I'm a gun owner, and I have been since I was 12 years old," said Democratic Sen. Mike Johnston of Denver. "What is before us is not a constitutional question but a policy question."

Some Democrats have reported getting threatening emails and phone calls. As senators debated, a man accused of threatening one of the Democrats appeared in court to answer criminal charges. In an appearance just down the street from the Capitol, Franklin Sain's lawyer told a judge Friday that Sain's emails and calls to state Rep. Rhonda Fields were constitutionally protected political speech.

Back in the Senate, lawmakers slogged through the seven firearms bills while deeper philosophical barbs about gun rights peppered the debate.

"This is a day of dysfunctionalism," griped Republican Sen. Steve King of Grand Junction.

Democrats frequently cited the Connecticut school shooting and the Aurora theater shooting as they argued the limits are needed.

Arguing for the magazine ammunition limits, Democratic Sen. Mary Hodge said the change to Colorado's heritage and the potential inconveniences on gun owners paled in comparison to the pain of gun violence.

"This bill is merely an attempt to reduce the slaughter," Hodge said.

Democratic Gov. John Hickenlooper has said he would sign into law a magazine limit and a background-check expansion.

Talking to a group of high school journalists Thursday, Hickenlooper said he's keeping his options open.

"I'm not in any way an anti-gun person," the governor said.