Who appears to pose the most immediate threat to othello?

I believe the answer is the Turks.

Othello experiences 2 threats, the Turks and the inner demon.

The inner demon is a psychological struggle that lies in Othello's subconscious. Even though it might harm Othello in a way, it wouldn't be immediate.

The turks on the other hands could cause physical harms to Othello and could be considered as 'immediate'