The 20th century was a cataclysmic era for Jews — a time of cosmic tragedy, transcendent rebirth, mass migration and millions of individual journeys of every sort. Nobody knows that better this month than Senator George Allen of Virginia, a conservative Christian whose Jewish origins, hidden for a lifetime, popped out to ambush him in the midst of a critical re-election campaign. Allen’s inexplicable use of a North African Jewish slang insult on the campaign trail last summer was a rare bump in what promised to be an easy glide to victory. His clumsy response when he was asked about his rumored Jewish background — calling it an “aspersion” — turned a minor curiosity into a national embarrassment. Whether his political career will survive the gaffe was unclear at press time. What Allen, 54, ultimately makes of the discovery, only time will tell. But Allen’s back-story — the tale of how his mother, Etty, a Tunisian-born Jew, escaped the Nazis and vowed to leave behind her Jewishness — offers a sobering lesson for all of us. Nobody knows how many thousands or millions of Jews decided during World War II to discard the identity that Hitler had pronounced a capital crime. Some have since returned to their origins. Others never looked back. All of them are part of us, even the junior senator from Virginia.