What's the difference between dumfounded and dumfounder?

Dumfounded

Definition:

• (imp. & p. p.) of Dumfound

Example Sentences:

• (1) He won the leadership with a bigger landslide than Blair acheived 21 years ago, swept to office by a tide of Corbynmania that has dumfounded everyone at Westminster.
• (2) An unnamed but dumfounded Elysée adviser who was in an interview with Le Monde at the time, muttered that he'd been prepared for government crises but not "marital" ones.

Dumfounder

Definition:

• (v. t.) To dumfound; to confound.

Example Sentences:

• (1) He won the leadership with a bigger landslide than Blair acheived 21 years ago, swept to office by a tide of Corbynmania that has dumfounded everyone at Westminster.
• (2) An unnamed but dumfounded Elysée adviser who was in an interview with Le Monde at the time, muttered that he'd been prepared for government crises but not "marital" ones.