The last time U.S. President Barack Obama met Israeli Prime Minister Benjamin Netanyahu, it was obvious that the two men distrusted and despised each other. This time (March 5), their mutual dislike was better hidden, but the gulf between them was still as big, especially on the issue of Iran's alleged desire for nuclear weapons.
There is something comic about two nuclear-armed countries (5,000-plus nuclear weapons for the United States, around 200 for Israel) declaring that it is vital to prevent a third country from getting a few of the things too — particularly when that third country, Iran, has signed the Nuclear Non-Proliferation Treaty and still abides by it, while Israel has always refused to sign it. But never mind that.
What divides Obama and Netanyahu is a question of timing. Obama's "red line" is the point at which Iran "possesses" a nuclear weapon, which would not arrive for a couple of years even if Iran actually intends to make one. (American and Israeli intelligence services concur that it is not working on one now.)