Do something punitive and limited, like the missile strike year ago, sending a message but not really changing anything.

Do something punitive and big (like taking out part or much of Syrian President Bashar al-Assad’s air force) that would send a serious message and hurt the regime, but risks a Russian response — and might appear to get the U.S. involved in a difficult and risky, open-ended anti-regime effort.

Drop his aim of getting out of Syria, and commit to a modest, open-ended presence focused on preventing ISIS from reestablishing itself, and giving the U.S. a seat at the table.