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The White House staff secretary who resigned following allegations of domestic abuse has put a spotlight on "incredibly common" patterns of violence against partners, experts say.

The allegations surfaced Tuesday against Rob Porter, an influential senior aide in the Trump administration, from two ex-wives: Jennifer Willoughby and Colbie Holderness. Both told DailyMail.com that Porter was verbally and physically abusive, with the abuse beginning on their honeymoons. They confirmed their account of their allegations to NBC News.

Porter has denied the allegations as "simply false" and "outrageous."

"I have been transparent and truthful about these vile claims, but I will not further engage publicly with a coordinated smear campaign," Porter said. Some in the White House were quick to jump to his defense.

Regardless, experts say the case brings attention to how misunderstood domestic violence is, and shows how hard it is for women to speak out against a spouse.

Related: NBC THINK: Believing Rob Porter's denials of domestic abuse lets us ignore the dangers women face

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While domestic violence can begin at any point in a relationship, it's a "very common story that it's only after the couple are married that the violence, or certainly the more severe physical violence, begins," said Kiersten Stewart, director of public policy at Futures Without Violence, a national nonprofit dedicated to ending violence against women and children. She added that sometimes the abuser has been emotionally controlling or verbally abusive before then.

"There's no one trajectory of violence, but that is not uncommon at all," Stewart said.

Victims also feel less inclined to leave once they're in a long-term, committed relationship, said Cindy Southworth, the executive vice president of National Network to End Domestic Violence.

"You're not as likely to walk away because you're already invested. You're on your honeymoon," Southworth said.

Porter's ex-wives have not alleged abusive behavior prior to their honeymoons. In a blog post, Willoughby said Porter cursed at her on their honeymoon and a month later "physically prevented me from leaving the house." She also described Porter allegedly punching glass in front of her and yanking her out of the shower to yell at her, all the while presenting a wholesome public persona.

"Everyone loved him. People commented all the time how lucky I was. Strangers complimented him to me every time we went out. But in my home, the abuse was insidious. The threats were personal. The terror was real. And yet I stayed," she wrote.

The experts say a dual personae is often seen in abusers, and makes the victim less believable when she comes forward.

"That's incredibly common and, sadly, why abusers often get away with it for so long," Stewart said. "It's one of the things that women who are victims struggle with the most. They're often just not believed. So often, people say, why doesn't she just leave or try to get help? She often does. But people don't believe her."

Domestic violence is alarmingly common: One in four women will experience severe physical violence from a partner at some point in her lifetime, according to the National Domestic Violence Hotline. But experts fear it's misunderstood.

"I do think that we struggle with the perception that we solved domestic violence, that this is a problem of the past, or that certain groups of people struggle with it, and that's not true at all," Stewart said.

In reality, according to Southworth of National Network to End Domestic Violence, "It cuts across every education and income level, race, class — you name it."

Domestic violence isn't only physical, although many people, including victims themselves, mistakenly believe it to be, Southworth said. Victims often dismiss other abusive tactics, such as a husband forbidding his wife from seeing her family or friends, that predicate any physical violence.

"There are other subtle things happening, and because they're so subtle, they're not so obvious," she said.

And domestic abuse isn't an anger problem, even though it sometimes appears like one.

"Instead, it's this deep-ingrained belief that 'I'm entitled to do this to you because I own you,'" Southworth said.