Bob Berg, the owner of Bob & Tom's gun shop, sits behind the counter of his store in October. Discussion lately has centered on a ballot initiative to require background checks for all gun purchases in Maine. ( Katie Zezima/The Washington Post)

The regulars at Bob & Tom’s Gun Shop spend hours here fiddling with firearms, sipping coffee and making small talk — chatter that now focuses on fighting an initiative that would require universal background checks for nearly all gun purchases in the state.

“It’s honest gun country here,” said Bud McLaughlin of Medway, Maine, who brought his 12-gauge shotgun into the shop, which is filled to the brim with rifles, shotguns, handguns, semiautomatic weapons and boxes of ammunition. Two rolls of toilet paper — one bearing the face of President Obama, the other of Democratic presidential nominee Hillary Clinton — hang from a shotgun that dangles from the ceiling.

“Once they start getting their fingers into the gun laws, it’s the first of the bullcrap that’s going to start,” he said.

But McLaughlin and his friends are likely to be disappointed on Tuesday. Voters here and in Nevada are poised to approve background checks for almost all private sales and transfers of guns. The ballot initiatives seek to close a loophole in federal law that exempts private sales — such as those online or at gun shows — from comprehensive checks.

In California and Washington state, which have already closed the loophole, voters are being asked to take gun control a step further. Washington will vote on whether to allow family members to seek a temporary order barring a person from having a gun if the person is determined to pose a risk to themselves or others. In California, residents will be asked whether they want to ban the sale of high-capacity magazines and require background checks for ammunition purchases.

The sign outside Bob & Tom's gun shop in Mattawamkeag and a show of support for defeating a ballot initiative to require background checks for firearm sales in Maine. (Katie Zezima/The Washington Post)

The four measures are part of a state-focused approach that gun-control advocates have adopted in the wake of repeated losses in Congress — a strategy reminiscent of the one pursued by same-sex marriage advocates beginning a decade ago. In Maine and Nevada, the legislatures passed background check bills that were vetoed by Republican governors, while California and Washington have already shown strong popular support for gun-safety rules.

“In the wake of Congress’s failure . . . we decided to take a state-by-state approach,” said John Feinblatt, president of Everytown for Gun Safety, a group backed by billionaire and former New York City mayor Michael R. Bloomberg. “In many ways we were borrowing a page from the marriage equality movement.”

Everytown has poured $13.3 million into Nevada, $4.6 million into Maine and $550,000 into Washington; it has not put any money toward the California initiative. The National Rifle Association has spent millions to oppose the initiatives, while also spending money in battleground states to help GOP Senate candidates and Republican presidential nominee Donald Trump.

Proponents of the measures ­argue that universal background checks are needed to keep guns out of the hands of people who might fail a check but could still obtain a gun through the loophole. Eighteen states and the District of Columbia require background checks for some types of firearm purchases.

“That’s the way to protect the Second Amendment, by keeping guns away from knuckleheads who are going to make the rest of us gun owners look bad,” said Nick Wilson, executive director of the Maine Gun Safety Coalition.

In Nevada, gun-control advocates have butted up against a potent force: the state’s law enforcement community. Sixteen of Nevada’s 17 sheriffs have come out against the ballot measure, as have Gov. Brian Sandoval and Attorney General Adam Laxalt, both Republicans.

Many in Nevada law enforcement said they don’t agree with language in the measure that requires a background check for the transfer of any gun at any time, requiring both people to go to a licensed firearms dealer before it can be exchanged. The measure exempts some temporary gun transfers, such as while hunting and during organized contests, from this requirement.

Chuck Allen, the sheriff of Washoe County, said he and others believe the requirement will create more work for stretched law enforcement agencies that would have to spend time making sure transfers were done legally.

The Maine provision has exemptions for shooting ranges, competitions and transfers while hunting or trapping.

Robert Uithoven, who is spearheading the NRA’s effort in Nevada, said the Nevada measure “would make illegal the common activities of people throughout the West and particularly in Nevada who are ordinary, law-abiding citizens. Transferring firearms, perhaps between cousins and good friends while going out recreating, shooting . . . those everyday common practices in Nevada would be illegal.”

A Las Vegas Review-Journal poll conducted in late October shows that 54 percent of Nevadans surveyed support the background check question, with 38 percent opposing.

Mark Prentice, a spokesman for Americans for Responsible Solutions, a gun-control group founded by former congresswoman Gabrielle Giffords (D-Ariz.), who was shot in 2011, and her husband, astronaut Mark Kelly, said that there is an appetite for change in states including Nevada.

Prentice and other gun-control advocates said they see education as a large part of their push. Many people, he said, don’t know that the loophole exists.

Giffords and Kelly have embarked on a 42-day, 16-state bus tour to push for gun control. The couple has been to Maine and Washington and plans to visit Nevada before Tuesday.

In Maine, a Portland Press-Herald poll conducted in late September showed that 61 percent of respondents support the background check measure, with 33 percent opposing.

“The public is fed up with the inability for politicians to take ­action,” said David Farmer, who works for Mainers for Responsible Gun Ownership. The group said it has 1,500 volunteers canvassing in the more-liberal population centers of South Portland, Brunswick and Orono and has spent thousands on ads.

But at the gun shop here in rural Mattawamkeag — about 60 miles north of Bangor and west of the Canadian border — owner Bob Berg sat behind the counter of his shop, boxes of ammunition stacked behind him and a sign reading “Guns left at own risk” tacked to a plywood wall next to an array of handguns. He said he doesn’t want outside interests controlling his state.

“It’s not what Maine needs,” he said of the expanded background checks.