Once he had joined the party he retook his tasks in the capital district of Los Mártires and assembled a team that helped him get elected for two consecutive terms as City Councilman (1990–1994).

In 1999 Vargas Lleras became the visible head of the opposition in the Senate to the government of president Andrés Pastrana, mainly due to the ill-fated 1999–2002 FARC–Government peace process.

His staunch opposition to ongoing peace talks in midst of those circumstances, brought him nearer to Álvaro Uribe Vélez, a dissident liberal candidate for the presidential election of 2002 who was calling for the end of the Demilitarized Zone of San Vicente del Caguán.

Vargas Lleras moved to support Uribe's candidacy, a decision that forced him to go against the Liberal party and its official candidate for the presidency Horacio Serpa.

In 2002 he ran for his third term of office in the Senate on the ticket of the political movement Colombia Always, a dissident of the Liberal Party, founded by Juan Lozano.

[2] In July 2005, the national news magazine Semana published a report stating that the Office of the Attorney General of Colombia pointed a man called Joaquín Vergara Mojica, an ex guerilla member of the ELN terrorist organization as the one behind the bomb-attack against Senator Vargas Lleras.

However, on June of the same year he resigned his senate seat in a move to try to save the political reform law, in face of the crisis triggered by the fact that Lara Restrepo could not vote it for risk of being accused of legal bias.

[3] The Cambio Radical party was implicated in a so-called "parapolitics" scandal when there were allegations og ties between the paramilitary group AUC and politicians.

In 2012 the "parapolitics" scandal was reported on again when Inspector General Alejandro Ordoñez announced that there would be an investigation into the alleged ties between Vargas and jailed warlord Martin Llanos.

After a long campaign trail where he visited 30 of the 32 Departments of Colombia, Vargas Lleras gradually launched his government plan, calling for a number of politically important reforms.

In a video published in his Facebook account he thank the group of citizens who launched his presidential bid through the registration of a committee to collect signatures towards running for the presidency.

The Citizen committee was formed by Simón Vélez (architect expert on bamboo), Eduardo Pacheco (President of Grupo Colpatria and economist) and Jeison Aristizábal (founder of Asodivalle and chosen in 2016 as a CNN Heroes of the year] .

[6] This launch of the campaign surprised many politicians because he didn't use his political party to run (Radical Change) but instead started to collect signatures from citizens all around Colombia.