Reiss and other activists seeking to end the practice told NBC News that they hope the report could serve as a catalyst for Congress to address the issue once and for all. But they also say they worry lawmakers could continue to slow-walk efforts to pass legislation.

“Everywhere we go, legislators, staffers, domestic violence professionals are surprised we allow child marriages in almost every U.S. state,” Amanda Parker, senior director at the AHA Foundation, which advocates against forced marriages, told NBC News. “We think of this as a problem that happens somewhere else, and I think that’s where we get the disconnect.”

“The bigger question is: Why is this happening for something that seems like such a simple fix?" Parker added. "How is it that our United States government is essentially facilitating child marriages?”

The issue starts with federal law. The Immigration and Nationality Act does not set minimum age requirements for a minor to request a visa for an adult spouse or fiancée, or vice versa. Petitions are first considered by U.S. Citizenship and Immigration Services, an agency within the Department of Homeland Security.

If the petition is approved, the State Department then decides whether to issue a visa. Since USCIS considers only whether the age at marriage “violates the laws of the place of celebration or the public policy of the U.S. state in which the couple plans to reside," according to the Senate report, advocates say this is where the disconnect occurs.

New Jersey and Delaware are the only states that prohibit marriages to those under the age of 18. Both states passed the bans in 2018. Most states have laws that allow citizens under 18 to marry, but often with judicial or parental consent.

Between 2007 and 2017, USCIS approved more than 5,500 petitions by adults to bring minor spouses or fiancées to the U.S. and nearly 3,000 approvals for minors trying to bring in older spouses or fiancés, according to the Senate report. Girls were the minors in 95 percent of the cases, according to the data.

In one case, a 71-year-old requested entry for a 17-year-old spouse, and in another, a 68-year-old petitioned for a 16-year-old to come into the country, according to the Senate report. Both requests were approved. Other approvals include a person age 55 petitioning for a 13-year-old and several people well into their 40s requesting spouses as young as 14 or 15.

“The United States condemns child marriages overseas, but we are not taking the steps to condemn it within our own borders,” Parker said. “It’s an awareness problem first.”

The Senate report cited date entry errors and faulty processes at USCIS, particularly its reliance on a paper-based immigration benefits system, as the reason applications are not more thoroughly reviewed. It also noted that the State Department rarely rejects petitions approved by USCIS.

Brett Bruen, a former official in President Barack Obama's White House and foreign service officer, told NBC News in an interview that lapses also happen at the embassies and consulates where many of the requests are reviewed.

“What ends up happening is a lot of these embassies are told to just approve it and move on,” Bruen said. “Your bosses expect you to push these things through. They don’t want to deal with letters from Congress or calls from family members.”

Michael Bars, a spokesman for USCIS, said the agency "has taken steps to improve data integrity and has implemented a range of solutions that require the verification of a birthdate whenever a minor spouse or fiancé is detected."

"Ultimately, it is up to Congress to bring more certainty and legal clarity to this process for both petitioners and USCIS officers,” Bars added.

In a statement to NBC News, a State Department spokesperson said the department "takes this issue very seriously."

"We are committed to protecting the rights of children and combatting forced marriage," the spokesperson said. "We will not issue a visa until an applicant has proven that he or she is legally eligible to receive one. If an applicant needs additional screening or review for whatever reason, we will not issue the visa until that screening or review is complete."

Reiss says she thinks “simple, plain old sexism” is one reason that the issue isn’t taken as seriously as it should be, adding, “these are mostly male legislators we are going to.”

Parker also highlighted some of the pushback advocates get from lawmakers.

“You would be surprised at political responses when we have meetings with them,” she said. “It seems like everyone had a great grandpa and grandma who were married at 13 and they were married for many years, and they say, ‘I don’t think that my constituents will support raising the marriage age to 18.”

She added, “There will be a little more scrutiny on each of the cases just because of the report coming out, but it doesn't go far enough. We are incredibly hopeful Congress will take action to make this simple fix so that adults can only sponsor visas.”

Last year, Rep. Bobby Rush, D-Illinois, introduced legislation to end child marriages in the United States, but the bill never made it out of committee.

Rush said in a statement to NBC News that he will continue to work with his colleagues to take on the issue during this session of Congress.

“Like so many others, I was shocked to learn the extent of this issue and how our immigration system is complicit in perpetrating this atrocity,” he said. “I am committed to working with my colleagues to end this objectionable practice.”

Reiss said that as long as lawmakers fall behind in addressing the issue, she will continue to press them.

“I’m going to continue pushing and insisting that every state do what New Jersey and Delaware did, and that the federal government take basic steps to address the problem and to stop being complicit and actually encouraging child marriage,” she said.

“I’m going to keep screaming until the federal government is not complicit in child marriages anymore," she continued. "It’s 2019 for crying out loud. Child marriage is an ancient relic from our sexist past, and it doesn't have any place in our society.”