A group of House Democrats is demanding a new investigation into President Donald Trump’s deployment of troops to the southern U.S. border, calling the situation a forgotten but still problematic scandal for the White House and the military.

“The America people deserve to know why the Trump administration is still politicizing our military, and whether they are forcing (troops) to violate the law under these orders,” said Rep. Raul Grijalva, D-Ariz. “The troops should not be pawns in political games that are being played.”

About 5,000 troops are currently deployed to the U.S. border, more than half of whom are active-duty forces assigned to support roles for border enforcement activities.

That mission, which began a year ago, was mandated by Trump after Congress could not reach a deal on funding for his proposed southern border wall project, which critics have decried as expensive and anti-immigrant. Trump has argued the military presence is needed to make up for personnel and resources shortfalls in immigration control activities.

Defense officials have said they anticipate the mission (both the active-duty portion and the deployment of about 2,000 National Guardsmen) to last for several more years. But Democrats in Congress have questioned the legality of the mission, and on Friday called it an “armed human wall” for political purposes instead of national security needs.

The event re-upping the immigration controversy took place just a block away from the ongoing House impeachment hearings on Capitol Hill, where Democrats are investigating whether Trump withheld foreign aid to Ukraine for personal political reasons.

Democrats at the border event referenced those hearings but said the national attention on that controversy cannot overtake other troubling issues with the Trump presidency.

“We have to keep the focus on what they are doing, militarizing the border,” said Rep. Juan Vargas, D-Calif. “(The president) is using the military in a way that is completely illegal.”

The group, along with community activists, are requesting an inspector general investigation into whether Trump’s orders violate the Posse Comitatus Act, a 19th-century federal law that restricts active-duty military participation in domestic law enforcement activities.

Defense officials have dismissed those concerns in the past, but lawmakers said reports of shifting responsibilities and increasing tensions along the border have raised their concerns.

Rep. Barbara Lee, D-Calif. and a frequent critic of U.S. military operations overseas, said she also worries that the border mission amounts to the president “using the military as his own private militia” and said she wants a clear vote in Congress on the use of military force along the Mexican border if the mission is to continue.

Troops deployed to the region have been helping to construct and reinforce barriers along the border. On Thursday, CNN reported that the Pentagon in recent months rejected a request from the White House to construct a deep trench along the border to deter illegal crossings, citing the expense and usefulness of such an effort.