The gun debate has shifted dramatically. Suddenly, it looks as if the issue will benefit Democrats in November, not Republicans.

The reason for the shift doesn’t rest primarily on the intelligence and commitment of the students of Marjory Stoneman Douglas High School in Parkland, Florida, although many of them have been articulate and persuasive.

Nor does the shift naturally follow from the decisions of large American corporations to stop selling assault weapons, or to end partnerships with the National Rifle Association, although those steps are a significant development.

And the shift in gun control politics isn’t happening because, after mass shootings in places like Orlando, Las Vegas, Sutherland Springs, San Bernardino and Newtown, the attack in Parkland finally was the straw that broke the camel’s back.

No, the reason why the gun control issue was a big advantage for the GOP for decades but now favors the Democrats can be traced to the shift in the electoral coalitions of the two parties.

A red shift

For years, the gun control debate benefited Republicans because their party was able to attract gun rights voters who were — or had been — reliably Democratic. Those voters initially aligned with the Democrats because of the party’s commitment to organized labor and its working-class agenda, and they constituted an important part of the party’s base vote in places like northeastern and western Pennsylvania, Minnesota’s Iron Range, upstate New York and working-class areas of Ohio, Michigan and Wisconsin.

But as “cultural issues” — including abortion, school prayer, civil rights, gun control and ultimately gay rights and same-sex marriage — became increasingly salient from the late 1960s into the 1990s, a new fracture in American politics emerged.

Many cultural conservatives found themselves uncomfortable in the Democratic Party, and they started flirting with, and then shifting to, the GOP. Opponents of gun control — or advocates of gun owner rights, if you prefer — were among the most vocal party switchers.

By attracting former Democrats and swing voters who cared primarily about gun owner rights, the GOP was both adding to its numbers and subtracting supporters from the Democrats.

The gun issued changed the political arithmetic so completely in the Republicans’ favor that Democrats, increasingly located in the suburbs and in America’s cities, gave up on culturally conservative voters and decided the party should avoid talking about gun control if it hoped to woo any working-class whites.

A costly shift

But the shift of culturally conservative voters to the GOP has not been without its downside.

These voters, too often, helped make the party appear intolerant, mean-spirited and extreme, including on issues such as gun control. This eventually produced a new fracture in the electorate — and the emergence of a new crucial voting group, suburban voters.

The suburbs were, of course, once reliably Republican, whether they were in southeast Pennsylvania, in upscale counties outside New York City or in areas outside Washington, D.C.

The increasing cultural conservatism of the Republican Party made many suburban voters uncomfortable, but as long as the focus was on the liberalism of the Democrats (or the failures of Democratic incumbents), suburban voters usually stuck with the GOP.

But as Republicans moved right on cultural issues, many suburbs started to slide a bit more left.

Upscale Republican bastions, such as Montgomery County, Pennsylvania; Fairfield County, Connecticut; Nassau and Westchester counties in New York; Montgomery County, Maryland; and Fairfax County, Virginia, suddenly found themselves voting Democratic.

Now, suburban voters increasingly find that on guns they have more in common with their urban friends than with their rural ones. Some restrictions on guns, in particular, seem increasingly reasonable to swing voters after numerous mass shootings. As the issue has become more salient politically, it has also become potentially more effective for Democrats.

A winning shift

Of course, conservatives will point out that there are many pro-NRA voters, and “pro-gun” voters have tended to vote on one issue, guns, while supporters of gun control vote on a much broader range of issues.

The problem with that argument is that the party coalitions have changed.

Opponents of new gun controls are now so thoroughly integrated into the GOP that they are part of that party’s political base. Because they are no longer swing voters, they no longer have the electoral clout they once did.

Some Democrats from conservative, largely rural states or congressional districts will need pro-gun voters to win elections, and they will try to walk a fine line on the issue, as Conor Lamb is trying to do now in a western Pennsylvania House special election.

But in many states and districts, swing suburbanites — and particularly suburban women — are a much more important constituency than are NRA members because those suburban voters can decide which party wins — just the way anti-gun control voters once could.

This increased attention from suburbanites has changed the electoral equation for 2018, and that is why Democrats now should benefit from any focus on gun control issues.

Note: This column first appeared in Roll Call on March 6, 2018.