The Republican on Tuesday reiterated plans to put more than 1,000 National Guard members into action.
Last week, Defense Secretary James Mattis approved Pentagon funding for 4,000 members of the National Guard, until the end of September.
Trump says the Guard is needed to combat what he has called a crisis of migrant crossings and crime.More news: Finger find adds weight to earlier out-of-Africa timing
Nielsen is scheduled to visit new border wall construction efforts near the small town of Santa Teresa on Thursday. Some have chosen to remain in Mexico, but others have made a decision to try and continue to the U.S.
This week, an additional 300 service members are reporting to armories for required processing and training, prior to being equipped for the mission. Last week, the head of state said he wants to send between 2,000 and 4,000 National Guard members to the Mexican border, due to "the misrule that continues on our southern border".More news: Jimmy Kimmel apology for 'gay insult' on Sean Hannity tweet
While the Republican governors of Texas, New Mexico and Arizona swiftly agreed to President Trump's request to deploy the guard, the lone Democratic border state governor kept absolutely silent for a full week.
Gov. Doug Ducey suggested a gaggle of troopers making able to deploy from a Phoenix military base Monday that their "mission is about providing manpower and belongings" to assist companies on the border and denied that there was a political motive.
Pursuant to your request, the California National Guard will accept federal funding to add approximately 400 Guard members statewide to supplement the staffing of its ongoing program to combat transnational crime.More news: Loss making Deutsche Bank changes CEO to change image
Under the federal law Trump invoked in his proclamation calling for National Guard troops, governors who send troops retain command and control over their state's Guard members and the USA government picks up the cost.