“I am tired of seeing our Second Amendment rights trampled on. We can beat them.”

Now, after months of gathering signatures and skirmishing in court, gun activists in Colorado, with the support of the National Rifle Association, have forced Mr. Morse and a fellow Democrat, Senator Angela Giron, into recall elections. The recall effort is seen nationally as a test of whether politicians, largely Democrats, outside big cities and deep-blue coastal states can survive the political fallout of supporting stricter gun laws.

“Legislators should be scared,” said Becky Mizel, chairwoman of the Republican Party in the old steel and railroad town of Pueblo, Ms. Giron’s home district. “We have a battle here.”

Around his Colorado Springs-area district, Mr. Morse has spent the summer in campaign overdrive. He walks door to door, explaining his votes to people in his narrowly divided district…

“They’re going to turn out to ride me out of town on a rail,” Mr. Morse said. “Symbolically, if you could take me out, that would be a benefit to the special gun interests.”