Word for stealing the voice of the people and misrepresenting it for nefarious purposes

Say a group of people vote for a leader in an election but the leader then goes on to "speak for the people" but actually he's speaking for himself and his cronies. I'd like it to be clearly in a derogatory sense.

"Mr ..... claimed he was speaking on behalf of the people who voted for him but he was actually [stealing] their voice"

What word would best fit here?

You could use the term co-opt:

co-opt v. tr.
3. To take or assume for one's own use; appropriate: co-opted the criticism by embracing it.

From TFDO

The answer is in the title of your question

Misrepresent

to give a false or misleading representation of usually with an intent to deceive or be unfair

to serve badly or improperly as a representative of

For example:

He claimed he was speaking on behalf of the people who voted for him, but he was mispresenting them when he announced the new policy that would...

The most suitable word for my context was "Highjack" bringing strong, explicit implication of stealing for their own purposes. The word was contributed in a comment that was subsequently removed. Thanks to that unknown contributor!

How about pervert?

From Google search:

pervert verb: alter (something) from its original course, meaning, or state to a distortion or corruption of what was first intended

Your example:

Mr ..... claimed he was speaking on behalf of the people who voted for him but he was actually perverting their voice

It's hard to find a verb more derogatory than pervert, not to mention its other obvious connotations as a noun.

Also, as suggested by @alwayslearning, how about misappropriate?

From Dictionary.com:

misappropriate: to put to a wrong use

Your example:

Mr ..... claimed he was speaking on behalf of the people who voted for him but he was actually misappropriating their voice.