I'm not sure George Romney was a US Citizen after all.

[treestar]

49. the parents were born in the Us so they were citizens, however

did they live in the US enough time, before George was born, to pass their citizenship on to them?

If we are born and raised in the US and leave after age 18 we can pass our citizenship on.

But Gaskill was 13 and Anna Amelia unknown when they left the US - analyzed against the law at the time, they may not have had enough ties to the US to be able to pass their citizenship to foreign born children.

Romney's parents, Gaskell Romney (1871–1955) and Anna Amelia Pratt (1876–1926), were American citizens and natives of the Territory of Utah.[7][8][9] They married in 1895 in Mexico and lived in Colonia Dublán in Galeana in the state of Chihuahua (one of the Mormon colonies in Mexico), where George was born on July 8, 1907.[1][4][10]

So Gaskell was in Mexico at age of 24 and married Anna who was 19. George was born in 1907.

wiki:

Birth abroad to two United States citizens
A child is automatically granted citizenship if:
Both parents were U.S. citizens at the time of the child's birth;
The parents are married; and
At least one parent lived in the United States prior to the child's birth. INA 301(c) and INA 301(a)(3) state, "and one of whom has had a residence."
The FAM (Foreign Affairs Manual) states "no amount of time specified."
A person's record of birth abroad, if registered with a U.S. consulate or embassy, is proof of citizenship. They may also apply for a passport or a Certificate of Citizenship to have their citizenship recognized.
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Both his parents were US citizens at time of his birth, they were married, and Gaskill had lived in the US before George's birth.