Ask this question again, you're going to need a more specific time the president has done this. however, if you are asking about WWI, the USS Lusitania, the Zimmerman Telegram, German U Boats targeting American ships, and so on.
Jonas Salk<span> </span><span>was an American </span>medical researcher<span> and </span>virologist<span>. He discovered and developed one of the first successful </span>polio vaccines in the 1950's.
Hope I helped. :)
North America perceived the soviet as cultural and a economic threat
The answer is what you want to believe
