There is speculation in Colombian media that political party Cambio Radical are set to confirm an alliance with presidential candidate Juan Manuel Santos.
So far it is confirmed that six of the party’s eight senators are in favor of an alliance with the Partido de la U candidate.
The senators opposing the union are Alfonso Valdivieso and Rodrigo Lara.
Vargas Lleras was himself a candidate in the first round of Colombia’s presidential election, but did not gain enough votes to move into the second round election.
Santos, who gained the most votes in the first round, will go head-to-head with Green Party candidate Antanas Mockus in the June 20 runoff.