A divided Supreme Court offered measured support Wednesday for a federal law giving placement preferences to Native American families in adoption and foster care matters involving Native children.

The issue is a clash of tribal sovereignty, states' rights, and racial discrimination claims-- and it was clear in more than two hours of oral arguments the justices were affected by emotionally-driven points raised by lawyers on both sides.

At issue is whether the high court should toss out or severely dismantle the Indian Child Welfare Act of 1978, meant to protect Native American rights in state child custody proceedings. It has long been championed by tribal leaders as a means of preserving their families and culture. 

But a group of white families-- along with several states-- seeking to permanently adopt Native children say they are being discriminated and disadvantaged, in violation of equal protection guarantees in the Constitution.

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In more than three hours of spirited arguments the justices debated the legislative limits of a unique relationship between Native tribes and the federal government, and the ability of state courts to broadly determine the discretionary "best interests" of children in placement hearings.

"Congress understood these children's placement decisions as integral to the continued thriving of Indian communities," said Justice Elena Kagan. "And that's not something that we can second-guess, is it?"

But Justice Brett Kavanaugh addressed the racial discrimination claims.

"To get to the heart of my concern about this," he said, "you would agree that Congress couldn't give a preference for white families for white children, for black families for black children, for Latino families for Latino children, for Asian families for Asian children," in adoption or foster care matters.

Among those challenging the law-- Jennifer and Chad Brackeen of Fort Worth, Texas, who had first fostered, then adopted, a son known in court papers as A.L.M., beginning in 2016, after his mother, a member of the Navajo Nation was unable to care for him. The tribe sought to place the boy with other out-of-state tribal members not related to him. 

The Brackeens eventually won custody of A.L.M but now would like to adopt the child's half-sister, identified in state proceedings as Y.R.J.

"It's been three-and-a-half years in court, and we have not been able to finalize the adoption," Chad Brackeen told Fox News Digital. "Ultimately, these two siblings belong together."

But the more than three-fourths of the 574 federally-recognized American tribes told the Supreme Court in various amicus briefs the law has been on the books for 44 years and is working.

"The precedent of the Supreme Court is that Indian tribes are political groups of people, they are not racial groups of people," said Chrissi Ross Nimmo, the deputy attorney general of Cherokee Nation. "Tribes determine citizenship... just like countries." 

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Many tribes warn of a broader loss of political sovereignty if the ICWA is struck down or weakened, over such matters as healthcare, education, and housing, which are all covered under specific federal laws. 

Texas, along with Indiana and Louisiana have also challenged the federal law, saying it oversteps authority over state child custody matters.

In arguments, the court struggled to reconcile parallel claims over whether the federal law is discriminatory, and whether the federal government has plenary-- or unqualified-- authority over relations with Native tribes.

"Congress has permitted tribes to exercise power over environmental regulations that have indirect effects off reservation. That would seem to go too" if the ICWA law was struck down, said Justice Neil Gorsuch. "We have laws that promise Native Americans access to sacred sites off reservation and religious liberties off reservation. That would seem to go."

"We'd be busy for many years striking things down.... if this is the [judicial] line we're going to draw… Very, very busy," Gorsuch added.

But Justice Samuel Alito worried about the extent of congressional authority.

"Could Congress go further than it has gone in ICWA and say that an Indian child may not be adopted by a non-Indian couple under any circumstances?" he asked. "If there are limits, it's hard for me to see where the limits are. That's where I need help."

And Justice Amy Coney Barrett-- who with her husband Jesse have two adopted children from Haiti-- questioned a provision in ICWA that gives preference to Native adoptive and foster parents-- even if they are not in the same tribe as the child.

Alito, Kavanaugh, and Chief Justice John Roberts also questioned the lawyer for the Justice Department about that provision. Roberts and his wife Jane have also adopted two children.

The consolidated cases are Haaland v. Brackeen (21-376); Cherokee Nation v. Brackeen (21-377); Texas v. Haaland (21-378); and Brackeen v. Haaland (21-380). A ruling is expected in coming months.