Nazgul-Were they still Men?

[Sharkû]

Arguably, the sway Sauron had had on the Nazgûl since their 'enslavery' was too heavy to overcome for Saruman. However, that didn't prevent him from trying, and succeeding at least in improving his own standing:

"I will report this myself to the Lord of Barad-dûr," he said loftily, "to whom I speak from afar on great matters that concern us. But all that you need to know on the mission that he has given you is where 'the Shire' lies. That, says Mithrandir, is northwest from here some six hundred miles, on the borders of the seaward Elvish country." To his pleasure Saruman saw that even the Witch-king did not relish that. You must cross Isen by the Fords, and then rounding the Mountains' end make for Tharbad upon Greyflood. Go with speed, and I will report to your Master that you have done so."
This skilful speech convinced even the Witch-king for the moment that Saruman was a faithful ally, high in Sauron's confidence. At once the Riders left the Gate and rode in haste to the Fords of Isen." (UT, 3,IV,ii)