To be precise, the USA didn't allow people to practice dual citizenship as adults prior to the late sixties.
Do you understand the difference?
And the USA cannot block -- nor has ever tried to block -- another nation from exercising their own citizenship laws. If Canadian law called for Cruz to gain Canadian citizenship, neither Cruz nor the USA could keep them from so doing.
For that reason, many Americans who were born overseas after WW II were advised not to return to the country of their birth because they might be eligible for the draft -- as the country of their birth considered them citizens under their laws. This, despite their being full-fledged American citizens under our laws (and fully eligible to run for the Presidency, by the way).
born in another country... most likely to a foreign mother... and eligible as a ‘natural born citizen’?
whatever.
you’re not interesting in logic or law, just propaganda to try and boost your guy.