President Barack Obama will reprise his role of "consoler-in-chief" when he meets with families of those murdered in the San Bernardino, California, shootings.
Fourteen people died on December 2 when radicalised Muslims Syed Rizwan Farook and his wife Tashfeen Malik opened fire on Farook's co-workers at a holiday party.
Obama's visit on Friday evening will be "patterned after" a similar trip to Roseburg, Oregon, in October when he met for about an hour with families of victims of a shooting at a community college there, White House spokesman Josh Earnest said on Wednesday.
The president has visited the sites of other mass shootings, including Charleston, South Carolina and Newtown, Connecticut, seeking to console rather than express anger towards the killers.
Unlike the other visits, Obama will land in San Bernardino as local and federal authorities are still investigating the shooters, later killed in a gun battle with police, and whether they were inspired by foreign militant extremists.
"We are always conscious of the impact that a presidential visit could have on law enforcement or emergency response resources," Earnest said on Thursday.
FBI director James Comey has said the couple was radicalised some time ago. Authorities are also trying to determine whether Farook and Malik had help from others.
Federal authorities on Friday charged Enrique Marquez for providing material support to Farook and Malik. Marquez allegedly purchased two rifles used in the attack and had plotted to carry out attacks with Farook in 2011.
Assistant Attorney-General John P. Carlin said in a statement that Marquez is charged with conspiring to provide material support to terrorists "for his role in plotting attacks on American soil in 2011 and 2012, attacks which were, fortunately, not carried out".
Carlin said Marquez, 24, is also charged with a firearms violation for making a "straw purchase" of weapons for Farook.
According to an affidavit, Marquez told investigators he and Farook made plans to attack the library or cafeteria at Riverside Community College in California in late 2011.
He and Farook also planned to attack a state highway during peak hour with pipe bombs and shoot at law enforcement and emergency crews as they arrived.
The FBI also revealed investigators were looking into any connections there may have been between one of the two killers and four men arrested in 2012 in a separate terrorism case brought in nearby Riverside, California.
"I would not anticipate that a visit by the president just for a couple of hours to that community to console the families of the victims of that attack would have any impact on the pace or success of the ongoing investigation," Earnest said.
The attack has made Americans nervous, while Obama has tried to explain his strategy for combating Islamic State and preventing further attacks.
The president has used the attack to renew his call to tighter gun control, drawing criticism from some Republicans who say the administration should do more to fight terrorism than restrict guns.
Obama will stop in San Bernardino on his way to Hawaii, where he will spend the holidays with his family.
