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Under the National-Socialist regime, he and several members of his family were threatened by Nazis because of their Anti-Nazi views, and he had to flee twice, first to France and then to the Netherlands, where during the war he went underground and helped Jews to flee.
In later times, Gumpel expressed regret that well known Catholic personalities and groups questioned the wisdom of promoting the cause of Pius XII's beatification. For different reasons, Jewish groups too were opposed to the pope's beatification.