GOP governors respond to Trump's call to send Guard to border National Guard presence at the border will likely require governors' consent.

The governors of states bordering Mexico began to respond Thursday to President Donald Trump’s call for them to send National Guard troops to help secure the southern border.

Homeland Security Secretary Kristjen Nielsen said Wednesday her office had been in touch with each of the state governors about how to proceed with the president’s plan.

GOP governors responded positively, including Arizona's Republican governor, who tweeted his support even before Nielsen’s announcement.

“Arizona welcomes the employment of the National Guard to the border,” Gov. Doug Ducey tweeted Wednesday. “Washington has ignored this issue for too long and help is needed. For Arizona, it’s all about public safety.”

Arizona welcomes the deployment of National Guard to the border. Washington has ignored this issue for too long and help is needed. For Arizona, it’s all about public safety.

— Doug Ducey (@dougducey) April 4, 2018

Texas Gov. Greg Abbott, also a Republican, echoed Ducey’s support in a statement released Wednesday evening saying Trump's move “reinforces Texas’ longstanding commitment to secure our southern border and uphold the rule of law.”

“I welcome the support,” Abbott said.

A statement issued by the office of New Mexico Gov. Susana Martinez, another Republican, said she “appreciates the administration’s efforts to bring states to the table.”

In contrast, Democratic Gov. Jerry Brown’s office in California issued a statement saying it would review the request promptly as they waited for more details. Brown and several California cities have been in running immigration battles with the Trump administration.

John Cohen, an ABC News Consultant and former acting Homeland Security undersecretary, said for many governors funding is the biggest consideration.

“When you see a state say ‘we look forward to reviewing the details and understanding more the commitment that they’re looking for’, what they’re basically saying is ‘we’re not going to commit one way or another until you tell us how you’re going to offset these costs.”

Who foots the bill for the troops is largely determined by how the National Guard is ordered to the border.

Cohen said command of National Guard troops normally belongs to state governors. An agreement between the federal government and the state governors would mean that Guard troops remain under the command of the governors, with each consenting to assign specific troops to support border security. Under that arrangement, Cohen said, the federal government will likely help to offset the costs in some way.

According to federal law, the president does have the option of placing the troops under federal control, Cohen said, but only in situations where the nation is invaded or in danger of invasion, there is fear of rebellion or when regular forces are unable to enforce the law.

If the president were to federalize the Army National Guard, command of the troops would transfer from the governor of the respective states to the Pentagon, and the federal government would assume the total financial burden, Cohen said.

Neither the Department of Homeland Security nor the president has yet signaled an intention to federalize troops. Cohen said that could be because there’s not enough evidence to prove that the situation at the border is a severe threat.

“While this may be impressive political theater intended to resonate with his political base it's really unclear what threat they are trying to address,” Cohen said.

But a statement released by the Department of Homeland Security Thursday emphasized the threat. “We need to close these dangerous loopholes that are being taken advantage of each and every day, gain operational control of the border, and fully fund the border wall system,” the statement said. “As the President has repeatedly said, all options are on the table.”

Trump is not the first president to suggest the deployment of National Guard troops to the border. In fact, both President Barack Obama and President George W. Bush did the same during their presidencies. In both cases, troops were deployed through agreements with the state governors, not through federalization of the Guard.

While the border states have been responsive, not all state governors are on board. Oregon Gov. Kate Brown, a Democrat, tweeted out against the call to send troops to the border on Wednesday.

“If @realDonaldTrump asks me to deploy Oregon Guard troops to the Mexico border, I’ll say no,” Brown Tweeted. “As Commander of Oregon’s Guard, I’m deeply troubled by Trump’s plan to militarize our border.”

If @realDonaldTrump asks me to deploy Oregon Guard troops to the Mexico border, I’ll say no. As Commander of Oregon’s Guard, I’m deeply troubled by Trump’s plan to militarize our border. — Kate Brown (@KateBrownForOR) April 4, 2018

If @realDonaldTrump asks me to deploy Oregon Guard troops to the Mexico border, I’ll say no. As Commander of Oregon’s Guard, I’m deeply troubled by Trump’s plan to militarize our border.