How can Ehud speak about victory as though it had already occurred?

Judges 3:28 (ESV)

28 And he said to them, “Follow after me, for the LORD has given your enemies the Moabites into your hand.” So they went down after him and seized the fords of the Jordan against the Moabites and did not allow anyone to pass over.

Ehud speaks this way for dramatic effect. His battle cry echoes the Lord's instruction to Judah (Judges 1:2).