David, this gentleman might like to know: I immigrated to Canada in the '60's, got Canadian citizenship in the early '70's, and assumed I was no longer an American citizen because I thought at the time that swearing allegiance to another government automatically voided one's U.S. citizenship. So I have behaved like a born Canadian ever since. I have visited a lot in the States, having family there. With the recent changes in mood in the States, I was interested to hear  from a friend in similar circumstances that we did not lose our U.S. citizenship, so I applied for and easily received a U.S. passport. I use it to go into the States, and my Canadian passport to come home. No problem, no questions. Feel free to pass this on to whoever wrote you.