President Donald Trump's decision Monday to step aside and let Turkish forces come into northern Syria instantly cast into doubt the fate of ethnic Kurds there who have been the United States' closest allies in the fight against the Islamic State group, and who had worked to achieve a degree of self-rule in that stretch of Syria.

Now, the question of who could provide a long-term deterrent to Iranian and Russian interests in the area — and help ensure that the Islamic State does not rebound in Syria — is suddenly very much in play again.

What now for US


What role do the Kurds play in Syria?

Why does Turkey want to invade?