The list of 'womanizers' in the WH goes as far back as Thomas Jefferson and Sally Hemmings. As a rule (in the past) 'these things' were kept out of the limelight by the press (JFK's womanizing for example) as a 'gentleman's agreement' with a few notable exceptions. President Grover Cleveland had a 'love child' and it didn't stop him being elected, despite his opponent's scurrilous rhyme:
"Ma, Ma, where's my Pa?
Off to the White House, ha ha ha!"
As a rule I think we Americans tend to separate a person's ability to govern well from his 'peccadillos', feeling that marital infidelity is a 'personal matter' between the Pres and the First Lady and that it does not affect his ability to run the country. I'm not saying this is right or wrong, just that it 'seems that way'.