DENVER » Two years after Colorado tightened its gun laws in response to mass shootings at a Connecticut elementary school and a suburban Denver movie theater, newly empowered Republicans here at the state Capitol are trying to repeal those measures, reviving an emotional debate over gun violence.

Once again, the Legislature has become a stage for protests and wrenching testimony from families of people cut down by bullets. Lawmakers are sparring over Second Amendment freedoms and public safety, and arguing about the effectiveness of new measures that expanded background checks and reduced the size of ammunition magazines.

In the state Senate — where Republicans, by one vote, won a majority in November’s elections — measures to undo the new background checks and allow legal gun owners to carry concealed handguns without a permit advanced this week after a committee vote split along party lines. The Republican measures are almost guaranteed to die in the Democratic-controlled House or be vetoed by the governor, a Democrat, but Republicans said they were following through on a core ideological issue.

"Philosophically, we are fully committed to our constitutional rights and believe they were needlessly and gratuitously infringed upon," said Bill Cadman, the Republican Senate president. "We’ve made a solemn commitment to restore them."

Looming over the debate is the trial of the gunman who killed 12 people and wounded 70 others inside an Aurora movie theater in July 2012, one of the worst mass shootings in U.S. history. As lawmakers here vote on a flurry of gun bills, lawyers in a suburban courthouse 15 miles away are sifting through questionnaires submitted by thousands of potential jurors as they prepare for opening arguments of what is expected to be a monthslong murder trial of the gunman, James E. Holmes.

That shooting touched thousands of lives in the Denver area, from the scores of victims and witnesses inside the crowded theater to the hundreds of emergency workers, doctors and nurses, and friends and classmates of the victims. Some families who have embraced tougher gun regulations say they are feeling the strains of fighting another political battle over guns while the trial grinds forward.

"It just flies in the face of reasonableness," said Dave Hoover, whose nephew AJ Boik was among those killed. "Here we are, dealing with the pain of reliving it. It never goes away. It will never go away."

The gun legislation votes highlight the partisan clashes of a newly divided state government. While Republicans and Democrats said they would be able to pass bipartisan spending measures and advance bills on simpler issues — such as banning a powdered form of alcohol and fining people convicted of animal fighting — both sides said they would stand their ground when it came to guns, gay rights and other issues that lay bare Colorado’s urban-rural divide.

As Republicans advanced gun bills in the Senate, House Democrats, who hold a majority on the other side of the gold-domed Capitol, killed five pro-gun measures. And while Senate Republicans trumpeted their efforts to undo 2013 green energy requirements passed by Democrats, House Democrats sent out a news release crowing that four more Republican-sponsored bills "bite the dust."

Democrats have vowed to quickly defeat other pro-gun legislation and repeal measures as they advance.

"Absolutely no chance," said Dickey Lee Hullinghorst, the Democratic House speaker, assessing those measures’ odds of passage. "This is one of the controversial issues where we’re never going to agree."

In early 2013, in the wake of the shootings in Aurora and at Sandy Hook Elementary School in Connecticut, Gov. John W. Hickenlooper and Democrats who controlled the Colorado House and Senate passed a slate of gun control laws over the nearly unanimous objections of Republicans. They banned online-only training for concealed weapons permits, required people to pay for their own background checks, limited the size of ammunition magazines to 15 rounds and required background checks on private, person-to-person gun sales.

Gun control advocates hailed the passage of these laws as a major victory in a heartland state. Conservative lawmakers said the measures would not prevent mass shootings and that they chiseled away at the Second Amendment. One company, Magpul, a manufacturer of ammunition magazines, left the state in protest.

"Disarming law-abiding citizens who can defend themselves doesn’t make anyone safer," said Cadman, the Senate president.

Republicans also say the gun restrictions pose a political risk for rural Democrats in a state where elk and deer hunting is an autumn pastime and where a backlash over the 2013 gun measures cost two Democrats their seats in recall elections. But the issue may be losing some of its political punch.

The two staunchly pro-gun Republicans who won seats in the recall elections were themselves ousted in November, one of them losing to a former staff member of Mayors Against Illegal Guns. And the debate at the Capitol has drawn smaller, less volatile crowds than those who spilled out of hearing rooms two years ago, when planes displaying pro-gun banners flew over the Capitol.

State Rep. Rhonda Fields, a Democrat who received racist and threatening letters and emails after she became a leading supporter of tighter gun measures in 2013, said the issue still split Democrats and Republicans. But she said Coloradans were still buying guns, that background checks were proceeding and that most people appeared to be largely unbothered by the new laws.

"The Capitol isn’t as noisy," Fields said. "We have just taken the sting out of this argument."

Jack Healy, New York Times

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