 He opposed the separatist efforts of José Antonio Páez, and according to the publication "Entorno Inteligente", the triumvirate presidential model Mendoza helped initiate in 1811 was "bitterly criticized by Simon Bolivar in his Cartagena Manifesto, [with the model reflecting an] ideology of liberal constitutionalism which prevailed in the United States..."

Mendoza was a loyal and trusted advisor to Simon Bolivar, and he collected documents on Bolivar's public life, publishing 20 small volumes of the documents between 1824 and 1828.Bolivar purportedly stated about Mendoza that ""you are the man I admire most in this world, because you carry and retain the model of virtue and helpful goodness.