The debate highlighted a fundamental philosophical difference between many Democrats and Republicans. The Democrats' leader in the House, Dickey Lee Hullinghorst, said he resented "the implication that unless we all arm ourselves, we will not be adequately protected."
But one of the Democrats who voted against party lines, Democratic Rep. Ed Vigil, said that his decision was rooted in the state's history.
"This is part of our heritage. This is part of what it took to settle this land. I cannot turn my back on that," he said.
Vigil's decision represents some of the hold that history has on the West, which a political generation ago swung to the right.
But the vote Monday in Colorado's gun control debate is part of the shift in the region's politics to the left, including the legalization of marijuana in Washington state and Colorado. Washington also upheld the legality of gay marriage in November.
Democratic Rep. Dominick Moreno, who represents a district in suburban Denver and was among the four lawmakers called by Biden, said the vice president "emphasized the importance of Colorado's role in shaping national policy around this issue."
Democrats in the Colorado House have a 37-28 advantage, giving them enough leeway when some members of their party side with Republicans. The gun control measures go next to the state Senate, where Democrats will need more unified support because their advantage is only 20-15. Republicans need only three Democrats to join them to defeat the bills.
The state's Democratic governor, John Hickenlooper, supports the expanded background checks and thinks gun buyers should pay for them. He also said he may support limits on the size of magazines, if lawmakers agree to a number between 15 and 20.
He said he hasn't decided whether to support banning concealed firearms on campuses and stadiums.
Republican Rep. Christ Holbert became emotional while explaining his opposition to the bills. He said he understood Fields' support of the bills, given her district and her son's shooting death.
"But I care passionately about the United States Constitution and the constitution of this state, and the oath that we have taken," Holbert said.