Donald Trump examined eight different styles of walls on the US border with Mexico, prototypes for the barrier he promised to build to keep out illegal immigrants and drugs.
The Republican brought a tough message on immigration to California during his first visit as US president to the heavily Democratic state that has served as a base of resistance to many of his policies.
Standing beside the prototypes, as US border patrol agents rode nearby on horseback, Mr Trump discussed the merits of various designs with border officials, his chief of staff, John Kelly, and Homeland Security Secretary Kirstjen Nielsen.
“The border wall is truly our first line of defence,” Mr Trump told reporters.
Mr Trump has asked the US Congress for $18 billion to build the structure, but the funding has become ensnared in controversy over a host of immigration restrictions he and Republicans have proposed.
On the other side of the border, in Tijuana, Mexico, residents laughed off the idea the monolithic slabs will stop desperate immigrants.
“The wall is just a waste of money. People will continue to cross, here, there, and everywhere,” Salome Pacheco said.