Complex sentence: Mayor Jaime Castro finished his term with a low popularity rate, but he was capable of rearranging the city's financial structure, and began a period of surplus, which continued during Antanas Mockus term.
Split into simpler sentences: Mayor Jaime Castro finished his term with low popularity, but was able to rearrange the city's financial structure. This led to a period of budgetary surpluses, which continued during Antanas Mockus term.