Democrats and advocacy groups are slamming a House Republican bill to reauthorize the Violence Against Women Act, saying it could actually cause more harm than good to victims of domestic violence.

“House Republicans have again decided to pursue a partisan, ideological agenda at the expense of the safety of America’s women, children and families,” House Minority Leader Nancy Pelosi (D-Calif.) said on her website Tuesday.

Critics were buoyed Tuesday when the White House threatened to veto the House bill.

But the rhetorical war on the issue has masked a surprisingly complicated legal debate at the center of the groups’ complaints, with Republicans warning that long-standing legal precedent and civil liberties protections are at risk.

The Republicans’ concerns were buoyed by a Congressional Research Service report dated Tuesday that said under a Senate-passed version of the bill the “Constitution will not apply” for prosecutions of U.S. citizens for domestic violence crimes committed on tribal lands.

The tribal issue is the most thorny of three top concerns by the coalition of advocacy groups, which agreed on a Tuesday conference call to lobby fiercely against the House bill, spurning overtures from House Republicans and a managers’ amendment designed to address their concerns.

“This is an extremely dangerous bill” that victims rights advocates “shouldn’t go anywhere near,” said Lisalyn Jacobs, a top official for the National Task Force to End Sexual and Domestic Violence Against Women.

The two other main concerns about the House bill, which was introduced by Rep. Sandy Adams (R-Fla.), are that it changes provisions in current law regarding domestic abuse of illegal immigrants and  that it does not include new provisions to protect gay, lesbian and transgender  people who were in the Senate bill.

At stake on the tribal issue is a loophole for crimes committed on tribal lands that shields some domestic violence perpetrators from prosecution. Criminals have learned to target the loophole, leading to alarmingly high rates of domestic violence in Indian Country, experts say.

On tribal land, American Indian tribes only have jurisdiction over crimes if the perpetrator is an American Indian. Meanwhile, most states only have jurisdiction when neither the victim nor the perpetrator is American Indian.

“Perpetrators can commit these crimes and know that they won’t be held accountable,” said Terry O’Neill, president of the National Organization for Women.

To close the loophole, the Senate bill would “recognize and affirm” the “inherent” authority of tribal courts to prosecute non-American Indian domestic violence perpetrators.

While seemingly simple, the language — specifically its reference to the “inherent” authority of the tribal courts — would overturn an influential 1978 Supreme Court case, Oliphant v. Suquamish Indian Tribe, and legally void several constitutional protections for U.S. citizens prosecuted under the new rules, according to the CRS.

The Supreme Court has long ruled that tribes have “inherent” authority to prosecute crimes committed by American Indians but no such authority to prosecute crimes perpetrated by non-American Indians. Because the tribal lands are considered legally sovereign, prosecutions under the “inherent” authority are not bound by the Constitution or Bill of Rights.

Congress could delegate authority to prosecute crimes, requiring it be used pursuant to the Constitution.

But the CRS report says that by affirming the “inherent” tribal authority to prosecute domestic violence crimes, the Senate bill would put those prosecutions in the same category as the sovereign prosecutions of American Indians.

“If Congress is deemed to delegate its own power to the tribes to prosecute crimes, all the protections accorded criminal defendants in the Bill of Rights will apply. If, on the other hand, Congress is permitted to recognize the tribes’ inherent sovereignty, the Constitution will not apply. Instead, criminal defendants must rely on statutory protections under the Indian Civil Rights Act or tribal law,” the report says.

Under the Indian Civil Rights Act or tribal law, “defendants may be subjected to double jeopardy for the same act; may not be able to exercise fully their right to counsel; may have no right to prosecution by a grand jury indictment; may not have access to a representative jury of their peers; and may have limited federal appellate review of their cases,” the report says.

Senate Minority Whip Jon Kyl (R-Ariz.) and Senate Judiciary ranking member Chuck Grassley (R-Iowa) raised issues about the tribal provisions during the Senate debate of the bill. Calling the section “blatantly unconstitutional,” Kyl said the bill “breaks with 200 years of American legal tradition that tribes cannot exercise criminal jurisdiction over non-Indians.”

The House Republicans’ managers’ amendment would allow American Indian victims to petition a federal district court for a “protection order” against the person alleged to have committed the domestic violence. Victims rights advocates unloaded on the change, calling it not nearly enough to stop an epidemic of tribal violence.

O’Neill characterized the GOP objections as an unwillingness to “trust Native Americans to uphold the Constitution,” adding that there’s “no evidence” tribal courts would not.