Obama's speech Thursday, in which he said Israel's pre-1967 borders, with land swaps, should be the outline for a Palestinian state, was condemned by Republicans and followed by a notably chilly meeting with Israeli Prime Minister Binyamin Netanyahu at the White House Friday.
Addressing the American Israel Public Affairs Committee, Obama reaffirmed "unbreakable" bonds and "ironclad" U.S. commitment to Israel's security.
He touted continued major U.S. military aid, including the new Iron Dome anti-missile system, which Israel has used to stop rockets from Gaza.
But he warned "the status quo is unsustainable" as the Arab population under Israeli control grows and the Jewish state's legitimacy is being increasingly questioned.
Obama knew his comments on 1967 would rouse controversy, he said, but "the current situation ... does not allow for procrastination."
He said his statement was nothing new and followed Clinton administration peace proposals.
"It means that the parties themselves … will negotiate a border that is different than the one that existed on June 4, 1967. It is a well-known formula to all who have worked on this issue for a generation."