Please answer a question about the following article about Chihuahua (state):

Under threat from the conservative forces, Governor Terrazas was deposed, and the state legislature proclaimed martial law in the state in April 1864 and established Jesús José Casavantes as the new governor. In response, José María Patoni decided to march to Chihuahua with presidential support. Meanwhile, Maximilian von Habsburg, a younger brother of the Emperor of Austria, was proclaimed Emperor Maximilian I of Mexico on April 10, 1864 with the backing of Napoleon III and a group of Mexican conservatives. Before President Benito Juárez was forced to flee, Congress granted him an emergency extension of his presidency, which would go into effect in 1865 when his term expired, and last until 1867. At the same time, the state liberals and conservatives compromised to allow the popular Ángel Trías take the governorship; by this time the French forces had taken control over the central portions of the country and were making preparations to invade the northern states.

Which president was forced to flee?
President Benito Juárez