Complex sentence: Despite her own involvement in politics, his mother tried to dissuade him from entering politics, due to his childhood struggles with asthma, believing that the stress of campaigning would be detrimental to his frail health.
Split into simpler sentences: Despite her own involvement in politics, his mother tried to dissuade him from entering politics, due to his childhood struggles with asthma. She feared that the stress of campaigning would be detrimental to his frail health.