First, one must clarify that the liberal party Escobar entered was not the main one but rather and split of the main party. Since 1958 when the dictatorship ended until the 1970's there was an agreement between the conservative and liberal party to alternate power. In this panorama, a young politician named Luis Carlos Galán considered a renewal of the liberal party ideas and in 1979 created a split party called the New Liberalism and it's with this movement that he entered the 1982 Colombian legislative elections.

However, Galán denounced Escobar after proofs of Escobar drug trafficking were presented to him and was expelled from the party. But a politician named Alberto Santofimio welcomed Escobar to his split movement of the main Liberal party: The Liberal Alternative but he was elected as an alternate so he didn't have much voice in the political debates at the House of Representatives. Eventually, Galán's friend, Rodrigo Lara Bonilla, also a member of the New Liberalism was chosen by the conservative government as Minister of Justice and from his position led the investigations of Escobar links to organized crime and bribery in high spheres of power.

Escobar didn't care about politics at all at least of what we know about him. He had two main goals: One was to keep a facade to divert the attention of his drug-related business and the other was to avoid the approval of the extradition treaty with the U.S that would have meant the drug leaders would have been judged with harsher authorities and not bribable as the ones in Colombia. Yes, he also built the neighborhood Medellin without slums but more as a mean to gain support by the poor people than with a political motive.

Sources

The Life and Crimes of Pablo Escobar-JD Rockefeller.

And these ones are in Spanish but can help you understand also why Escobar later planned and executed the murder of Galán.

https://www.eltiempo.com/archivo/documento/MAM-1633817

https://www.elespectador.com/especiales/el-sacrificio-y-impunidad-el-caso-galan-articulo-374565