Clintons infidelity is not in doubt at this point.  But just like Republicans overlook Trumps lying, incivility and the clear emotional imbalance, the Democrats do the same thing with Bill Clinton and his sexual exploits and Hillary's role in the cover up.    The same things happen in private lives every single day.     

Is is right for us to expect politicians to be 'better' than the rest of us?

Both parties cover up/attack because of high levels of partisanship and campaign financial sources that don't want their image soiled.   Elections aren't so different from sporting events, but most sports have clear rules of play and consequences on the field.

If you don't win elections you lose power.   Image is important to winning elections.    We should all be skeptical of what we see/hear.