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 Senate president, a Republican. “We’ve made a solemn commitment to restore them.”