It was an October surprise — or was it? Earlier in the month, Cal Cunningham, the Democratic Senate candidate in North Carolina, confirmed that he had an extramarital relationship with a California woman. Affairs like this used to end political careers, but Cunningham’s surprising resilience suggests we may be in a new era: one in which voters are more willing to think about politics transactionally, and partisanship covers a multitude of sins.

Polling data from North Carolina tells the story clearly — North Carolinians dislike Cunningham’s affair, but they aren’t changing how they plan to vote because of it.

The clearest data comes from Monmouth University. Before news of the affair broke, 34 percent of North Carolina voters viewed Cunningham favorably, and 22 percent viewed him unfavorably. Afterward, his favorability rating dropped to 25 percent, and his unfavorability rating jumped to 33 percent.

But at the same time, 51 percent of the state’s voters told Monmouth the relationship was “an issue for him and his family.” Cunningham’s lead over Republican Sen. Thom Tillis expanded by three percentage points among registered voters from his showing in Monmouth’s previous survey.

A similar pattern shows up in other public opinion research. In a New York Times/Siena College poll, Cunningham’s net favorability rating dropped, but his lead over Tillis remained steady. And, according to SurveyUSA, some seniors and women moved away from Cunningham, but he made up the ground with other groups. SurveyUSA puts him ahead by 10 points, and the RealClearPolitics average has him leading by four.

Cunningham’s affair was troubling to North Carolinians — but it appears they think that other things matter more. Most of Cunningham’s supporters are committed to ousting Tillis or to enacting parts of Joe Biden’s proposed agenda, so they’re willing to look past the transgression and stay in Camp Cunningham.

These numbers don’t mean that politicians have moral carte blanche. Voters take other wrongdoings, such as sexual assault, very seriously. Republican Roy Moore lost a winnable Senate election after The Post reported allegations that he initiated a sexual encounter with a 14-year-old girl when he was 32. Al Franken (D-Minn.) was pressured to leave the Senate after multiple women accused him of sexual misconduct. Ethical scandals matter, too — the Trump administration has been rife with corruption and self-dealing for years, and that’s part of the reason the president’s reelection bid is in such bad shape.

But these numbers do suggest that the penalty for extramarital relationships between consenting adults has decreased significantly.

Over the past few decades, a bipartisan parade of unfaithful men — led by Presidents Trump and Bill Clinton — has depoliticized marital infidelity. Yes, most Americans think extramarital affairs are wrong, and they don’t like it when politicians cheat. But politicians have also lost moral credibility on marriage and relationships, so much so that many voters no longer take their moralizing seriously. Democrats defend Clinton; Republicans defend Trump; and any politician who tries to stone an adulterer is immediately (and rightly) exposed as a partisan hack.

It’s not clear whether this new state of affairs is good for America. It’s easy to envision a downward spiral in which partisanship sands off the penalties for more behaviors, such as corruption and self-dealing. It’s also possible to imagine a future in which voters care less about the personal lives of their leaders, find new role models for their kids, and focus solely on the qualities, policy positions and competencies that are most relevant for the job.

For now, we know that voters are more jaded about affairs. Whether or not that’s good news for America, it’s great news for Cal Cunningham.

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