President Trump said he expects to decide in the next two weeks whether or not to authorize using the U.S. military in the conflict between Israel and Iran.

U.S. President Donald Trump initially distanced himself from Israel’s surprise attack on Friday that triggered the conflict, but in recent days has hinted at greater American involvement, saying he wants something “much bigger” than a ceasefire.

Aside from a potentially game-changing American intervention that shapes the fate of Iran’s nuclear program, two factors will help decide the length of the Israel-Iran war: Israel’s reserve of missile interceptors and Iran’s stock of long-range missiles.