Complex sentence: He ran for a second term in 2011, but failed to advance in the primary election and became the first Kansas City mayor since the 1920s to lose a re-election bid in the primaries.
Split into simpler sentences: He ran for a second term in 2011, but failed to advance in the primary election. This made him the first Kansas City mayor since the 1920s to lose his re-election bid in the primaries.