In some states you have to be careful about ‘write in’ voting. I was told by a poll worker ( the one handing out ballots ) that if you ‘wrote-in’ anyone that didn't register in advance as a ‘write-in candidate, it was a spoiled ballot and wouldn't be counted. That protest ‘Donald Duck’ vote would cause your entire ballot to never be counted. That could void all your down ticket votes. If in doubt of your state law/rules on write-in voting, leave that slot blank. An under vote won't spoil a ballot.
I didn't know that until a couple years ago when I asked about any write-in’s that might be running in a local race.
The lady was nice enough to explain the state law on it.
I then kicked myself for the times in the past I had voided my entire ballot with a silly write-in protest vote.
I think it varies from state to state how it is handled.