[El Gato]

As I pointed out earlier, Arthur’s father was not a US citizen until Arthur was in his teens. Didn’t matter then

It wasn't KNOWN then, so how could it have mattered?

[Mr Rogers]

“It wasn’t KNOWN then, so how could it have mattered?”

It had to be known. If they moved close enough to Arthur’s birth for the birthplace to be in question, then they HAD to know Arthur’s father did not live in the US for many years prior to Arthur’s birth.

[BP2]

It wasn't KNOWN then, so how could it have mattered?

Exactly.

Just because a former president was able to keep the wool over the American public's eyes until after he left office and burned all of his personal papers on his death bed, Chester Arthur's successful yet temporary deception does NOT set precedence for the British subject who's in office now.