On Wednesday, eight House Republicans voted with Democrats in favor of legislation that would require a universal audit of gun sales, despite opposition from the gun lobby.
Almost all Republicans who broke with their party are centrists, including several who represent competing neighborhoods.
The number of GOP defectors was only slightly higher than the five Republicans who had co-sponsored the legislation.
The legislation would require universal background checks for the sale of firearms, including in gun shows and private online transactions. Current legislation only requires licensed gun dealers to conduct a background check before making a sale.
But it provides for exemptions in certain circumstances, including transfers between family members, their use in hunting and when they are "necessary to prevent imminent death or serious bodily harm", such as domestic violence.
Democrats also plan to target King, Mast and Upton in 2020, while Smith, Buchanan and Diaz-Balart are considered safe seats for the GOP.
Mast was reelected last November by 9 points. He went beyond the idea of extending background checks to a stricter gun control measure: a ban on assault weapons.
Golden, a freshman, said he opposed the law because it sounds like a voting initiative that Maine voters rejected in 2016.
"Maine is neither Chicago, nor Washington, nor New York." For many of my constituents, access to firearms is a necessary part of everyday life and we have a tradition of possessing firearms. Responsible firearms, "Golden said in a statement.
"To ensure that criminal criminals do not have guns, we need to strictly enforce the existing system of background checks and provide them with the resources to work," he added.