Does voting for a non-Muslim candidate in the presidential elections, when there is a competing Muslim candidate, contradict the teachings of Islam?

It is not permissible to nominate a non-Muslim for the presidency when a Muslim candidate is available, because it is unanimously forbidden for a disbeliever to rule over Muslims, as Allah Almighty says: (And never will Allah grant the disbelievers a way against the believers). The conditions for Imamate (leadership) are: Islam, being a mukallaf (accountable adult), male, capable, free, and sound in senses and limbs. It is also not permissible for a Muslim to participate in an act that raises the morale of a disbeliever or in which a disbeliever is chosen as a ruler over Muslims; because that is considered loyalty and support for them. You have erred by prioritizing the disbeliever over the Muslim. However, if there is no Muslim candidate, and Muslims see a benefit in voting, then there is no harm in them nominating whoever is more beneficial to Muslims or less harmful to them.