No. It’s a stupid question.
And there are stupid answers.
Even if you vote for someone and say you held your nose, simply admitting that means you want that person to win, relative to the other candidates.
That is an endorsement. That is saying, “I want this person to win”.
Now, if you want to argue “degree” of endorsement, that is another matter.
Voting for a person and saying you did is an endorsement. The only exception is if you qualify it and say that, though you voted for them, you don’t want them to win. Protest votes would be an example.
And it could have been a protest vote against Mitt.