So I don't believe that the Witchking could do that whatsoever.
Of course the fiend couldn't do that to Gandalf the White. The idea alone is laughable.
He wouldn't even be able to break Gandalf the Grey's staff; note that Gandalf the Grey fought off 5 Nazgûl alone on Weathertop and defeated a Balrog.
The Nazgûl's only power is fear; (s)he who does not fear them, cannot be defeated by them - granted, though, if this person possesses the necessary combat prowess. Did Gandalf fear the Nazgûl? I think not.
Extrapolating from this, Aragorn would also have been able to defeat the Witch-King of Angmar with Andúril.
On a less serious note, the Witch-King was beaten by a GIRL, for Pete's sake... so he's clearly a weenie who would stand no chance whatsoever against the Wizard of wizards. So why the argument? :tongueelf:
Give up the Halfring, she-elf...