Muslims in medina did not support Imam Ali (A) against usurpers as if they forgot the word of the Prophet (P) about Ali (A) and his sermon in Ghadir. Several protests have been registered by him indicating that had Imam had real and sufficient supporter he would have waged a war against usurpers.
If Imam Ali (A) was appointed as immediate successor to the Prophet by Divine Order why did not he stand out against the usurpers? Here are three important reasons: Firstly, he did not have real and adequate supporters and few people backed him; otherwise he would have launched a war. Secondly, if he proclaimed a war the society would have been involved with a civil war which was very dangerous for Islam as a new established religion and moreover, Islam was targeted by threats from different directions. Thirdly, he preferred to resist and fought with the usurpers in negative way. His wife Fatimah (S) and he showed their dissatisfaction and annoyance with the establishment. [1]
[1] see: Nahj al-Balagha, sermon, 2,3,etc , Bihar al-Anwar, vol. 43, p. 209