Then there should be a link to it somewhere. Your links and others only showed one direction.
Yes it is. It's right there.
Migrants were not asked PROVE, the were only asked to renounce. In fact, current law encourages still encourages it. Says there could be problems with it.
And, of course, it's also Cruz Sr's track record. He didn't have to renounce Canadian citizenship when he took US citizenship, but he did.