Top Democrats have joined a number of Republicans in challenging President Obama’s policy toward Israel, further exposing rifts that the White House and its allies will seek to mend before next year’s election. The differences, on display as senior lawmakers addressed a pro-Israel group late Monday and Tuesday, stem from Obama’s calls in recent days for any peace deal between Israel and the Palestinians to be based on boundaries that existed before the 1967 Arab-Israeli war, combined with “mutually agreed swaps” of territory. Senate Majority Leader Harry M. Reid (Nev.), House Minority Whip Steny H. Hoyer (Md.) and other Democrats...