The largest, most mobilized block of single-issue voters has been, for the last several decades, pro-life voters. Pro-lifers, who typically identify as conservative Christians, were a large part of Donald Trump's victory in 2016. While Trump has, for most of his public life, eschewed religion and even called himself "very pro-choice," he spent a large amount of the 2016 election courting pro-life voters, promising to put conservative justices on the Supreme Court in hopes of overturning Roe v. Wade. He was rewarded with 81 percent of the white evangelical vote.
Abortion was not always an animating issue for conservatives. As Katherine Stewart writes for the Nation, conservative leaders in the 1970s worked together to find an issue that could unify southern voters. After deciding on abortion, conservative politicians and religious leaders cooperated to manipulate voters into rallying behind that one issue.
It took some time for the Republicans and the religious leaders to settle on abortion as the vehicle for consolidating political power. The breakthrough came when savvy religious activists, such as Weyrich and Jerry Falwell, noticed that the language used to express concerns about abortion was in essence the same language used to articulate anxieties about evolving family, gender, and racial norms. Republicans realized that by turning abortion into a matter of “family values,” they could make the cause of switching party affiliation attractive, especially to their white working-class base. Strategists for the Republican Party approached Falwell and encouraged him and his peers to organize evangelicals into a “Moral Majority” that would promote a pro-family social and political agenda. Declaring that abortion is “murder according to the word of God,” Falwell disseminated this message to the millions of evangelical voters through sermons, radio segments, and mailers.
Yet, after the election of President Trump, whose positions on immigration, guns, pollution and civil rights are decidedly un-Christian, many former pro-life voters are breaking from their single-issue habit. The New York Times profiled several evangelical Christians women in the reliably red state of Texas, all of whom backed Democrat Beto O'Rourke in the state's midterm elections.
All of them go to similarly conservative churches in Dallas. All are longtime Republican voters, solely because they oppose abortion rights. Only one broke ranks to vote for Hillary Clinton in 2016. But this November, they have all decided to vote for Mr. O’Rourke, the Democratic upstart who is on the front line of trying to upend politics in deep-red Texas.
...“I care as much about babies at the border as I do about babies in the womb,” said Tess Clarke...confessing that she was “mortified” at how she used to vote, because she had only considered abortion policy. “We’ve been asleep. Now, we’ve woke up."
While most single-issue voters have historically been Republicans, Democrats have recently found their own single issue to rally behind: gun control. Per a June 2018 poll from NBC News and the Wall Street Journal, roughly one-quarter of voters said gun control was a major factor in who they cast their votes for. Of these voters, 58 percent wanted to see Democrats take control of Congress.
In 2015, after a gunman killed 10 and wounded seven at Umpqua Community College in Roseburg, Oregon, a frustrated President Barack Obama made a bold suggestion to gun control advocates: Become “single-issue voters.”
The idea, he said, was that the powerful gun lobby already has a base of voters who put the Second Amendment ahead of all other issues — and if proponents of sensible gun control want to match them, they’ll have to do the same.
“You have to make sure that anybody who you are voting for is on the right side of this issue,” Obama said. “And if they’re not, even if they’re great on other stuff, for a couple of election cycles you’ve got to vote against them, and let them know precisely why you’re voting against them. And you just have to, for a while, be a single-issue voter because that’s what is happening on the other side.”
As has been seen with the success of pro-life candidates, voting based on a single issue is an effective way to bring your issue to the nation's consciousness and put your candidates in office. Liberal voters are hoping to do just that by voting based solely on candidate's views on gun control. Per The Washington Post:
They are setting up voter-registration tables at gun-control marches and are working to galvanize the nation’s youngest voters around a single issue.
“By voting in the midterms, I will choose to vote for senators and representatives who do not support the NRA,” said Kira Pomeranz, a senior at T.C. Williams High School in Alexandria, who registered to vote in February and will turn 18 in August.
...“Who here is going to vote in the 2018 election?” David Hogg, a Parkland survivor, asked at last month’s rally in the District. “We are going to make this a voting issue. We’re going to take this to every election, to every state, to every city.”