PIERRE, S.D. — Saying a private foundation has stepped forward to foot the bill, South Dakota Gov. Kristi Noem will send an unspecified number of National Guard members — though, no more than 50 — 1,200 miles south to the U.S. border with Mexico to help, according to her office, "secure the border" from a surge in migrant crossings.

Noem announced the deployment on Twitter on Monday, June 28, following up with a statement on Tuesday morning saying the state would respond to a call from Texas Gov. Greg Abbott, a Republican, who earlier this month joined Arizona Gov. Doug Ducey in writing to 48 other governors calling for law enforcement personnel and resources to patrol the international border.

Noem's announcement, which describes a "national security crisis" at the southern border, comes a week after neighboring Iowa Gov. Kim Reynolds announced she'd dispatched some two dozen state patrol officers to the border for two weeks at Texas officials' request.

The decision to send South Dakota Guard members has raised questions of how the operation is being funded. Initially in Tuesday's release, Noem's office said the deployment "will be paid for by a private donation."

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A follow-up question on the reason for the private funding — and whether this suggested the mission was outside the scope of the National Guard's role — was answered by Ian Fury, Noem's spokesman, who said that the "donation was made by Willis and Reba Johnson's Foundation" directly to the state government.

A public records search finds that Willis Johnson is a billionaire businessman and supporter of Republican politicians.

"The soldiers will be on a state active duty mission," said Fury, who added Noem welcomes any further donations to cut down the deployment's cost to state taxpayers.

State Sen. Reynold Nesiba, D-Sioux Falls, slammed the deployment Tuesday, saying the state's Guard members serve "our state and country."

"I extend my sympathy to the 50 South Dakota families who have become a tool for our governor's political aspirations and those of some anonymous political donor," Nesiba said.

Noem has been mentioned as a possible contender for the Republican nominee for president in 2024, though her office has denied she has any intention on running.

The deployment also drew criticism from Cheyenne River Sioux Tribal President Harold Frazier, who noted in a statement that Noem had previously denied a request made last year to establish medical facilities in preparation for the pandemic.

"I have a question for Gov. Kristi Noem," Frazier said. "Why did you not deploy soldiers at my request within the borders of the state of South Dakota during a national emergency but are willing to send them to do the work of private donors over a thousand miles away?"

Since President Joe Biden took office in January, America's southern border has seen a dramatic upswing in migrants from nations to the south. The influx has been seen by some analysts as a reflection of Biden's decision to nix a border wall and review the previous administration's controversial "remain in Mexico" policy. Earlier this month, Vice President Kamala Harris visited Guatemala and addressed potential migrants at a news conference, saying "Do not come. Do not come."

In Tuesday's announcement, Noem's office said the deployment would last "for between 30 and 60 days."