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When Vice President Biden arrived in Israel on March 8, seeking to smooth U.S. ties with the Netanyahu government and jump-start peace talks, he began by reaffirming America's "absolute, total, unvarnished commitment to Israel's security." The nearly simultaneous announcement by Israel that it plans to build another 1,600 homes in disputed East Jerusalem was not the warm embrace he was expecting.

Biden's riposte -- that Israel's actions threaten U.S. interests in the region and possibly endanger U.S. military forces there -- was a rare public admission that U.S. and Israeli interests are not identical. And the predictable accusations that followed the diplomatic slap heard 'round the world have exposed a growing rift in the pro-Israel community in the United States, between...