The day that President Trump ordered the withdrawal of American troops from Syria, the Islamic State claimed that it had set off a bomb in Raqqa, the group’s former capital, killing a Kurdish fighter.

It was a small, isolated attack, but the Islamic State’s boast was a canny assertion of the stakes in the American withdrawal — and an indication that the group was looking forward to exploiting a changed reality in Syria.

The United States withdrawal announced Wednesday is seen by analysts as an abandonment of America’s key allies in Syria, the Kurdish-led Syrian Democratic Forces, and a boon for the Islamic State — which still controls territory in southeastern Syria, is believed to still have thousands of fighters there and has continued to carry out attacks.

The withdrawal is also expected to give a green light to Turkey to carry out its threatened invasion of northeastern Syria, a move likely to draw Kurdish forces from the fight against the Islamic State in the southeast.