A graduate of the Higher University of San Andrés with extensive postgraduate studies, Santamaría entered the political field as a partisan of the National Unity Front and served as the party's municipal leader for La Paz.

In parliament, Santamaría split with National Unity, reorienting himself towards the Social Democratic Movement and establishing a close personal relationship with colleague Rafael Quispe, whose party, Somos Pueblo, he joined.

[1] As part of their shared pact, UN and the MDS had given one another ample autonomy to define their own electoral lists in the regions where they held the highest presence, giving La Paz-based UN greater sway over UD's candidates in the department.

[5] Promoted to full leader the following year,[6] Santamaría's term contended with the eternal divisions of the UD caucus, a grouping that operated less as a unified force and more as a collection of competing parties.

[7] Given the task of wrangling opposing factions, Santamaría faced criticism for his apathetic leadership style, opting to travel abroad while legislators back home squabbled amongst themselves over important committee assignments.

[31] Despite initial expectations that he would remain in the position for the duration of the transition,[32] Santamaría ultimately held the post for just one day,[33] as Áñez soon reversed course and reappointed Murillo.

Although Somos Pueblo's not-insignificant third-place finish did net it representation in the legislature, Santamaría's bottom-of-the-list placement on the party's electoral slate meant that he was not among those elected.